Lignan
Encyclopedia
The lignans are a group of chemical compound
s found in plant
s. Lignans are one of the major classes of phytoestrogens
, which are estrogen
-like chemicals and also act as antioxidants. The other classes of phytoestrogens
are the isoflavones and coumestan
s. Plant lignans are polyphenol
ic substances derived from phenylalanine
via dimerization of substituted cinnamic alcohols (see cinnamic acid
), known as monolignol
s, to a dibenzylbutane skeleton 2. This reaction is catalysed
by oxidative enzyme
s and is often controlled by dirigent protein
s.
Many natural products, known as phenylpropanoid
s, are built up of C6C3 units (a propylbenzene skeleton 1) derived from cinnamyl units just as terpene
chemistry builds on isoprene
units. Structure 3 is a neolignan.
Some examples of lignans are pinoresinol
, podophyllotoxin
, and steganacin.
When part of the human diet, some lignans are metabolized to form mammalian lignans known as enterodiol
(1) and enterolactone
(2) by intestinal bacteria
. Lignans that can be metabolized to form mammalian lignans are pinoresinol
, lariciresinol
, secoisolariciresinol
, matairesinol
, hydroxymatairesinol, syringaresinol and sesamin
.
. Other sources of lignans include cereals (rye
, wheat
, oat
and barley
- rye being the richest source), soybean
s, cruciferous vegetables
such as broccoli
and cabbage
, and some fruits, particularly apricots and strawberries.
Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Pinoresinol and lariciresinol are more recently identified plant lignans that contribute substantially to the total dietary lignan intakes. Typically, Lariciresinol and pinoresinol contribute about 75% to the total lignan intake whereas secoisolariciresinol and matairesinol contribute only about 25%. This distribution may change as the contributions of syringaresinol and hydroxymatairesinol have not properly been quantified in foods.
Sources of lignans:
A recent study shows the complexity of mammalian lignan precursors in the diet. In the table below are a few examples of the 22 analyzed species and the 24 lignans identified in this study.
Mammalian lignan precursors as aglycones (µg / 100 g). Major compound(s) in bold.
receptors and interfering with the cancer-promoting effects of estrogen on breast tissue. Lignans such as podophyllotoxin are therefore being studied for their possible effects on breast, prostate and colon cancer. Lignans are also good antioxidants scavenging free radicals
that may play a role in some diseases.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s found in plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s. Lignans are one of the major classes of phytoestrogens
Phytoestrogens
Phytoestrogens are plant-derived xenoestrogens functioning as the primary female sex hormone not generated within the endocrine system but consumed by eating phytoestrogonic plants...
, which are estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
-like chemicals and also act as antioxidants. The other classes of phytoestrogens
Phytoestrogens
Phytoestrogens are plant-derived xenoestrogens functioning as the primary female sex hormone not generated within the endocrine system but consumed by eating phytoestrogonic plants...
are the isoflavones and coumestan
Coumestan
Coumestan is an organic compound that is a derivative of coumarin. Coumestan forms the central core of a variety of natural compounds known collectively as coumestans. Coumestans, including coumestrol, a phytoestrogen, are found in a variety of plants...
s. Plant lignans are polyphenol
Polyphenol
Polyphenols are a structural class of natural, synthetic, and semisynthetic organic chemicals characterized by the presence of large multiples of phenol structural units...
ic substances derived from phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
via dimerization of substituted cinnamic alcohols (see cinnamic acid
Cinnamic acid
Cinnamic acid is a white crystalline organic acid, which is slightly soluble in water.It is obtained from oil of cinnamon, or from balsams such as storax. It is also found in shea butter and is the best indication of its environmental history and post-extraction conditions...
), known as monolignol
Monolignol
Monolignols are phytochemicals acting as source materials for biosynthesis of both lignans and lignin. The starting material for production of monolignols is the amino acid phenylalanine. The first reactions in the biosynthesis are shared with the phenylpropanoid pathway, and monolignols are...
s, to a dibenzylbutane skeleton 2. This reaction is catalysed
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
by oxidative enzyme
Oxidative enzyme
An oxidative enzyme is an enzyme that catalyses oxidation reaction. Two most common types of oxidative enzymes are peroxidases, which use hydrogen peroxide, and oxidases, which use molecular oxygen.They increase the rate at which ATP is produced aerobically....
s and is often controlled by dirigent protein
Dirigent protein
Dirigent protein is a protein which dictates the stereochemistry of a compound synthesized by other enzymes. Originally they were discovered in coniferous trees, where they participate in lignan biosynthesis. Lignan synthesis is catalysed by oxidative enzymes. In the test tube the reaction results...
s.
Phenylpropanoid
The phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the amino acid phenylalanine. Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of cinnamic acid, which is synthesized from phenylalanine in the first...
s, are built up of C6C3 units (a propylbenzene skeleton 1) derived from cinnamyl units just as terpene
Terpene
Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...
chemistry builds on isoprene
Isoprene
Isoprene , or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=CCH=CH2. Under standard conditions it is a colorless liquid...
units. Structure 3 is a neolignan.
Some examples of lignans are pinoresinol
Pinoresinol
Pinoresinol is a lignan found in Styrax sp. and in Forsythia suspensa. It is also found in the caterpillar of the cabbage butterfly, Pieris rapae where it serves as a defence against ants....
, podophyllotoxin
Podophyllotoxin
Podophyllotoxin , otherwise known as podofilox, is a non-alkaloid toxin lignan extracted from the roots and rhizomes of Podophyllum species. Under the trade name Condylox, a topical gel, it is used on the skin to treat external genital warts, caused by some types of the human papillomavirus...
, and steganacin.
When part of the human diet, some lignans are metabolized to form mammalian lignans known as enterodiol
Enterodiol
Enterodiol is a lignan formed by the action of intestinal bacteria on lignan precursors found in plants....
(1) and enterolactone
Enterolactone
Enterolactone is a lignan formed by the action of intestinal bacteria on lignan precursors found in plants. It acts as a phytoestrogen....
(2) by intestinal bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. Lignans that can be metabolized to form mammalian lignans are pinoresinol
Pinoresinol
Pinoresinol is a lignan found in Styrax sp. and in Forsythia suspensa. It is also found in the caterpillar of the cabbage butterfly, Pieris rapae where it serves as a defence against ants....
, lariciresinol
Lariciresinol
Lariciresinol is a lignan, a type of phenylpropanoids....
, secoisolariciresinol
Secoisolariciresinol
Secoisolariciresinol is a lignan, a type of phenylpropanoids....
, matairesinol
Matairesinol
Matairesinol is a plant lignan. It occurs with secoisolariciresinol in numerous foods such as oil seeds, whole grains, vegetables, and fruits.The plant lignans are precursors of the enterolignans...
, hydroxymatairesinol, syringaresinol and sesamin
Sesamin
Sesamin is a lignan isolated from the bark of Fagara plants and from sesame oil. It has been used as a dietary fat-reduction supplement, although no controlled studies on this application have been performed.-External links:***...
.
Food sources
Flax seed and sesame seed contain higher levels of lignans than most other foods. The principal lignan precursor found in flaxseed is secoisolariciresinol diglucosideSecoisolariciresinol diglucoside
Secoisolariciresinol diglycoside is an anti-oxidant phytochemical present in flax, sunflower, sesame, and pumpkin seeds. It is a precursor of mammal lignans and a phytoestrogen....
. Other sources of lignans include cereals (rye
Rye
Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
, wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, oat
Oat
The common oat is a species of cereal grain grown for its seed, which is known by the same name . While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed...
and barley
Barley
Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...
- rye being the richest source), soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
s, cruciferous vegetables
Cruciferous vegetables
Vegetables of the family Brassicaceae are called cruciferous vegetables. The vegetables are widely cultivated, with many genera, species, and cultivars being raised for food production such as cauliflower, cabbage, cress, bok choy, broccoli and similar green leaf vegetables...
such as broccoli
Broccoli
Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage"....
and cabbage
Cabbage
Cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...
, and some fruits, particularly apricots and strawberries.
Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Pinoresinol and lariciresinol are more recently identified plant lignans that contribute substantially to the total dietary lignan intakes. Typically, Lariciresinol and pinoresinol contribute about 75% to the total lignan intake whereas secoisolariciresinol and matairesinol contribute only about 25%. This distribution may change as the contributions of syringaresinol and hydroxymatairesinol have not properly been quantified in foods.
Sources of lignans:
| Source | Amount per 100 g |
|---|---|
| Flaxseed | 300,000 µg (0.3 g) |
| Sesame seed | 29,000 µg (29 mg) |
| Brassica Brassica Brassica is a genus of plants in the mustard family . The members of the genus may be collectively known either as cabbages, or as mustards... vegetables |
185 - 2321 µg |
| Grains | 7 - 764 µg |
| Red wine | 91 µg |
A recent study shows the complexity of mammalian lignan precursors in the diet. In the table below are a few examples of the 22 analyzed species and the 24 lignans identified in this study.
Mammalian lignan precursors as aglycones (µg / 100 g). Major compound(s) in bold.
| Foodstuff | Pinoresinol | Syringaresinol | Sesamin | Lariciresinol | Secoisolariciresinol | Matairesinol | Hydroxymatairesinol |
|---|---|---|---|---|---|---|---|
| Flaxseed | 871 | 48 | not detected | 1780 | 165759 | 529 | 35 |
| Sesame seed | 47136 | 205 | 62724 | 13060 | 240 | 1137 | 7209 |
| Rye bran | 1547 | 3540 | not detected | 1503 | 462 | 729 | 1017 |
| Wheat bran | 138 | 882 | not detected | 672 | 868 | 410 | 2787 |
| Oat bran | 567 | 297 | not detected | 766 | 90 | 440 | 712 |
| Barley bran | 71 | 140 | not detected | 133 | 42 | 42 | 541 |
Medicinal Uses
Lignans are capable of binding to estrogenEstrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
receptors and interfering with the cancer-promoting effects of estrogen on breast tissue. Lignans such as podophyllotoxin are therefore being studied for their possible effects on breast, prostate and colon cancer. Lignans are also good antioxidants scavenging free radicals
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
that may play a role in some diseases.
See also
- HerbalismHerbalismHerbalism is a traditional medicinal or folk medicine practice based on the use of plants and plant extracts. Herbalism is also known as botanical medicine, medical herbalism, herbal medicine, herbology, herblore, and phytotherapy...
- Naturopathic medicineNaturopathic medicineNaturopathy, or Naturopathic Medicine, is a form of alternative medicine based on a belief in vitalism, which posits that a special energy called vital energy or vital force guides bodily processes such as metabolism, reproduction, growth, and adaptation...
- NutritionNutritionNutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
- Phytonutrients