Lycopene: Functions

Lycopene represents the central substance in the biosynthesis of carotenoids. Through cyclization, hydroxylation, and further functionalization, lycopene can be converted into all other carotenoids. Like most carotenoids, lycopene has antioxidant properties. It represents the even most efficient natural scavenger of free radicals, especially peroxyl radicals – peroxynitrite – and singlet oxygen. For the deactivation of reactive oxygen compounds – process of “quenching” – lycopene has a higher rate constant than beta-carotene as well as vitamin E. In addition, carotene more effectively preserves cells and cell components from oxidative changes caused by hydrogen peroxide and nitrogen dioxide than beta-carotene. Despite its strong lipophilicity, lycopene can exert its protective effects on both lipophilic and hydrophilic compartments and organs. In order to be effective as an antioxidant in aqueous environments, lycopene requires proteins as a transport medium. By binding to the hydrophobic regions of the protein or to the lipid components of lipoproteins, the carotenoid is stabilized, transported, fixed and thus maintains its functionality in the aqueous medium. Finally, in addition to lipids, especially polyunsaturated fatty acids and cholesterol, lycopene can also protect proteins, enzymes, nucleic acids, carbohydrates as well as DNA from oxidative damage . As an essential component of cell membranes, lycopene influences their thickness, strength, fluidity, permeability and effectiveness. Even in relatively low concentrations, carotene forms a barrier against free radicals and protects the phospholipids of biomembranes from radical attack. In higher concentrations, however, lycopene can itself become a radical and have the opposite effect. If this is the case, there is an accumulation of oxidative cleavage products of lycopene, especially epoxides and apocarotenoids. These can lead to oxidative changes in the cell membrane and cell components, especially cellular DNA, and thus to oxidative stress. In addition, high levels of lycopene reaction products increase the permeability (permeability) of cell membranes, disrupting membrane integrity and increasing permeability to pollutants.

Lycopene and disease

Lycopene and tumor diseasesWith the help of numerous epidemiological studies, associations have been established between a diet low in fruits and vegetables and the development of tumor diseases. Accordingly, carotenoids, particularly lycopene, are thought to have a potential protective effect in relation to tumor diseases. Lycopene exerts its anticarcinogenic properties on all three stages of carcinogenesis (tumorigenesis)

  • Initiation phase – Due to the antioxidant effect, lycopene can scavenge free radicals and thereby prevent oxidative cell and DNA damage.
  • Promotion phase – lycopene stimulates communication between cells via gap junctions – cell-cell channels – allowing healthy cells to control the growth of precancerous cells
  • Progression phase – lycopene inhibits the proliferation and differentiation of tumor cells.

In 1999, Giovannucci summarized the English-language literature on the epidemiological studies conducted regarding lycopene and tumor diseases. The majority of these studies found an inverse association between tomato consumption or lycopene serum levels and tumor risk. Clear evidence of a chemopreventive effect of lycopene is available mainly for gastric, lung and prostate cancer. The protective effect is less pronounced for pancreatic, cervical, esophageal, oral, and colorectal carcinomas, as well as for breast cancer. Lung cancer studies from the state of Hawaii concluded that higher consumption of tomatoes among patients with lung cancer significantly increased survival. Other American cohort studies found a protective effect with regard to lung cancer only for lycopene and beta-carotene. No associations were discovered for other carotenoids. Colorectal cancerSome case-control studies found that increased intake of lycopene-rich foods reduced the risk of colorectal cancer by almost 60%.Carcinomas of the oral cavity, larynx and pharynxAccording to an epidemiological study from China, high tomato consumption is associated with about half the risk of oral carcinomas. Esophageal cancerA study from Iran reported a statistically significant 39% reduction in the risk of esophageal cancer with high tomato consumption, but only in men. In women, no protective effects of lycopene were found with respect to esophageal cancer. Prostate cancerA number of studies conclude that there is a strong correlation between increased intake of tomatoes or tomato products and protection against prostate cancer. The presence of high serum lycopene levels or high tissue concentrations of lycopene thus leads to a low risk of developing prostate cancer. In a randomized phase 2 clinical trial with lycopene administration prior to total prostate removal, lower tumor growth, a decrease in the concentration of prostate-specific antigen – PSA, a marker for an enlarged prostate – and a more pronounced synthesis of connexin 43, a regulatory protein of the gap junctions, were observed. In contrast, two studies did not confirm the chemopreventive effects of lycopene with regard to prostate cancer. Furthermore, lycopene exhibits protective properties with regard to bronchial carcinoma. In model and animal studies, lycopene suppressed the proliferation of endometrial, mammary gland, lung and prostate cancer cells. In some cases, apoptosis (programmed cell death) could be induced. The anticarcinogenic effects of lycopene are based, on the one hand, on its action as an antioxidant. By effectively protecting against cell membrane and DNA damage caused by reactive oxygen radicals, carotene inhibits tumor promotion. Lycopene provides a barrier not only to endogenous but also to exogenous carcinogens. Thus, it scavenges nitrogen dioxide radicals (NO2-) at least twice as effectively as beta-carotene. Secondly, lycopene has the ability to decrease the activity of IGF-1. The cell growth factor IGF-1 – “insulin-like growth factor 1″ – in high concentrations is a risk factor for breast and prostate cancer. It is assumed that lycopene can intervene in the mitotic circuit of IGF-1 and thus slow down the cell cycle. In doing so, the carotenoid increases the synthesis of a membrane-bound protein that downregulates the activation of the IGF-binding receptor. IGF-1 can still bind to the receptor, but can no longer initiate the signal transduction cascade. Other authors believe that lycopene rather inhibits the cell cycle by down-regulating the activity of cyclin-dependent kinases, cdk. Lycopene and Cardiovascular DiseaseLipid peroxidation-induced changes in low density lipoprotein (LDL) to oxidized LDL is considered a pathogenic factor in atherosclerosis (arteriosclerosis, hardening of the arteries). Since lycopene is an effective antioxidant, it can protect LDL cholesterol from oxidation by reactive oxygen radicals and thus inhibit the progression of atherosclerosis. In some scientific studies, lycopene in particular exhibited the most effective protection of all antioxidants tested against chemically induced lipid peroxidation of the liposome model. Elevated serum lycopene levels are associated with a low risk of atherosclerosis. In addition to antioxidant functionality, the cardioprotective properties of lycopene are based on modulation of atherosclerotic processes on vessel walls. To this end, lycopene reduces the expression of adhesion molecules on the cell surface. In addition, carotene reduces interleukin IL-1ß-stimulated and spontaneous adhesion of HAEC – human artificial episomal chromosome – to monocytes. Finally, lycopene can prevent deposits, for example of blood lipids, thrombi, connective tissue and calcium, in the walls of blood vessels, thus preventing atherosclerosis (arteriosclerosis; hardening of the arteries). Finally, lycopene acquires considerable importance in the prevention of cardiovascular disease. In a large European case-control study, the content of lycopene in adipose tissue was correlated with a protective effect against myocardial infarction (heart attack). Only lycopene, but not beta-carotene, has a slightly prophylactic effect against myocardial infarction. This effect has been confirmed several times by independent research groups.Sun protection effect – skin protectionThe skin protection effect of lycopene can be attributed to its antioxidant properties. Increased intake of fruits and vegetables containing lycopene is associated with an increase in skin lycopene levels. Lycopene is found in high concentration in the fibroblasts of the skin. There, due to its extreme lipophilicity, it is stored horizontally and thus transversely to the orientation of the phospholipids inside the cell membrane. In this way, lycopene protects many membrane molecules of skin fibroblasts, such as lipids and proteins, from oxidative damage by UV radiation and thus from UV-induced lipid peroxidation. Fibroblasts are cells found in all connective tissues of the body and play an important role in the synthesis of collagens and proteoglycans, the essential components of the extracellular matrix (extracellular matrix, intercellular substance, ECM, ECM) of connective tissues. Studies with skin fibroblasts revealed that lycopene is the most potent antioxidant of all carotenoids. It protected skin fibroblasts from aggressive UV radiation at levels six to eight times lower than beta-carotene and lutein. Finally, adequate intake of lycopene-rich foods can increase basic skin protection. Other effectsLycopene contributes to the strengthening of the immune system. Tomato juice intake may help to fully restore the immune system. This observation has only been made in people with very unbalanced diets, for example, when fruits and vegetables were completely avoided for a short period of time. In healthy, well-nourished people, on the other hand, increased lycopene intake did not lead to any increase in immune strength. Furthermore, according to epidemiological studies, lycopene exhibits surprising protective effects in hypertension (high blood pressure) and bronchial asthma.B

Bioavailability

Lycopene is relatively stable in storage. In addition, unlike lutein, it exhibits high heat resistance, which means that there is little loss during the treatment and processing of food, for example, during cooking. The bioavailability of lycopene from processed and heated tomato products, such as tomato juice and tomato soup, is significantly better than from raw tomatoes. This is because heating breaks the lycopene s bonds to proteins, dissolves crystalline carotenoid aggregates, and destroys cell assemblies. The bioavailability of lycopene can be further increased by suitable food preparation. Due to the strong lipophilicity of the carotenoid, the combination with fats and oils in warm dishes , for example, with olive oil, further favors the absorption of lycopene.

Functions in food

Lycopene finds application as a food colorant as a single substance or as a component of plant extracts. The carotene provides a red color and is found, for example, in soups, sauces, flavored beverages, desserts, spices, confectionery and baked goods. Furthermore, lycopene is an important precursor of flavoring substances. It is cleaved by cooxidation with the help of lipoxygenases, by reacting with reactive oxygen compounds and under thermal stress. Lycopene gives rise to carbonyl compounds with a low odor threshold. These degradation products play an essential role in the processing of tomatoes into tomato products.