Total anthocyanin and phenolic content of berry fruits.
Anthocyanin pigments are responsible for the red, purple, and blue colors of many fruits, vegetables, cereal grains, and flowers, increasing the interest due to their strong antioxidant capacity and their possible use to the benefit of human health. Abundant evidence is available about the preventive and therapeutic roles of anthocyanin in different kinds of chronic diseases. According to the structural differences and anthocyanin content of berries such as blackberry, blueberry, chokeberry, and others, there are different healthy properties in the treatments of circulatory disorders, cancer cell lines, and diabetes as well as antiviral and antimicrobial activities. On the other hand, molecular aspects play an important role in anthocyanin biosynthesis, making it possible to determine how biotic and abiotic factors impact its biosynthesis complex. Thus, the aim of this chapter was to describe the use of anthocyanins from berries for human health and their potential use as a pharmacological bioresource in the prevention of chronic diseases. In addition, an update of the molecular mechanisms involved in anthocyanin biosynthesis will be discussed.
- transcription factors
The scientific evidence regarding the positive relationship between diet and health has increased consumer demand for more information related to healthy diets, including fruits and vegetables, with functional characteristics that help to delay the aging process and reduce the risk of several diseases, mainly cardiovascular diseases and cancer . Berries are recognized as an important component of healthy diets due to their bioactive compounds. In this sense, commercial berry species such as blackberry (
Anthocyanins are natural pigments responsible for the blue, purple, red, and orange colors of many fruits and vegetables [8, 9]. Anthocyanins are a glycoside form of anthocyanidins , and the structural differences among them are related to the number of hydroxyl group, position, and kind and/or number of sugars linked to the molecule [10, 11]. These compounds appear to be an interesting natural resource of water‐soluble dyes because they are easily incorporated in aqueous media . Another important property of anthocyanins is their remarkable antioxidant activity, playing a vital role in the prevention of neuronal and cardiovascular illnesses, diabetes, cancer, etc. [11, 13]. Many reports have focused on the effect of anthocyanins in cancer prevention , human nutrition , and their biological activity . Nowadays, there is an increased interest in explaining the role of anthocyanins as a natural antioxidant and their mechanism of action on human health as well as the treatment of chronic diseases and their use as a natural dye, substituting the synthetic dyes, which can be toxic to humans. This review endeavors to describe the use of anthocyanins from berries for human health and their potential use as a pharmacological bioresource in the prevention of chronic diseases. In addition, an update of the molecular mechanisms involved in anthocyanin biosynthesis will be discussed. Finally, recent clinical and preclinical studies about anthocyanin use in the prevention of human diseases are reported.
2. Anthocyanin and phenolic compounds in berries
Phenolic acid, organic acids, tannins, anthocyanins, and flavonoids are phenolic bioactive compounds with a high concentration in the berry fruits . The chemical structure of phenolic compounds is characterized by one or more aromatic rings with hydroxyl groups. According to their structural characteristics, phenolic compounds are classified into five major groups: phenolic acids, stilbenes, flavonoids (flavonols or catechins, flavonols, flavones, flavonones, isoflavonoids, anthocyanins), tannins, and lignans . The concentration of phenolic compounds in berry fruits is altered by many factors, such as genotype, species, agronomic management, climatic factors, ripening stage, harvesting time, and postharvest management [17, 18]. Given the plant phenol attributes of berry species, attention has largely focused on anthocyanin and flavonol antioxidant action on human health. In this way, substantial epidemiological and experimental research suggests that intakes of recognized nutritional antioxidants such as vitamin E and carotenoids can decrease the oxidative damage of proteins, lipids, and DNA
It has been reported that the antioxidant capacity of flavonoids is stronger than vitamins C and E [21, 22], and under
|Scientific name||Common name||Cultivar||Anthocyanins*||Phenolics**||References|
|Red currants||London Market||7.8||1115|||
|Red currants||White Versailes||1.4||657|||
|Red currants||Ben Lomond||261||933|||
Anthocyanin concentration widely differs significantly among plant species, even among species of the same genus. In Table 1, anthocyanin and total phenolic compounds of different species and cultivars and their analysis are detailed. In blackberry, anthocyanin content is generally similar in all species, but phenolic content shows strong differences (Table 1). Anthocyanin content in
3. Molecular regulation of anthocyanin biosynthesis
Six structural genes are common in the anthocyanin pathway in all angiosperms, which are divided into two main groups. The first group is the upstream genes or early biosynthesis genes, for example, chalcone synthase (CHS), chalcone flavanone isomerase (CHI), and flavanone 3‐hydroxylase (F3H), coding for enzymes that produce precursors for one or more important non‐anthocyanin flavonoids. The second group is the downstream genes or late biosynthesis genes, for example, anthocyanidin synthase (ANS), dihydroflavonol‐4‐reductase (DFR), and UDP‐glucose flavonoid 3‐oxy‐glucosyltransferase (UF3GT), coding for enzymes specific to anthocyanin synthesis [30–32]. In the anthocyanin pathway, l‐phenylalanine is converted to naringenin by phenylalanine ammonia lyase (PAL), cinnamate 4‐hydroxylase (C4H), 4‐coumarate CoA ligase (4CL), chalcone synthase (CHS), and chalcone isomerase (CHI). Then, the next pathway is catalyzed by the formation of complex aglycone and anthocyanin composition by flavanone 3‐hydroxylase (F3H), flavonoid 3'‐hydroxylase (F3'H), dihydroflavonol 4‐reductase (DFR), anthocyanidin synthase (ANS), UDP‐glucoside flavonoid glucosyltransferase (UFGT), and methyl transferase (MT) . It has been described that the transcription of early and late biosynthesis genes to produce anthocyanins appears to be regulated by R2R3‐MYB and basic helix‐loop‐helix (bHLH, also known as MYC) called transcription factors in collaboration with tryptophan‐aspartic acid repeat (WDR) or WD40 proteins [32, 34–37].
3.1. MYB transcription factor
The MYB transcription factors involved in the flavonoid pathway have been identified and described for several kinds of model plants, crops, and ornamental plants. The first identified and reported MYB transcription factor in plants was in
3.2. Basic helix‐loop‐helix (bHLH)
After MYB, bHLH proteins, also known as MYC, are the second most important family of transcription factors involved in anthocyanin biosynthesis [34, 61]. The bHLH protein domain is constituted of about 60 amino acids and is characterized by the presence of 19 conserved amino acids, five in the basic region, five in the first helix, one in the loop, and eight in the final second helix . The basic region of bHLH has basic residues (5.8 on average) essential for DNA binding. In Arabidopsis, 20% of bHLH transcription factors do not have this domain and can act as a repressor because forming heterodimers are unable to bind to DNA . Two cis‐element boxes have been reported to bind with bHLH proteins, the E‐box (5'‐CANNTG‐3'), and G‐box (5'‐CACGTG‐3') elements. The G‐box is the most commonly recognized sequence representing 81% of the proteins predicted to bind DNA [61, 62]. In the basic region, two amino acids conferred the property on binding DNA in Arabidopsis plants. The Glu13 and Arg16 are the E‐box recognition motif . Glu13 has contact with CA bases of E‐box and Arg16, apparently helping Glu13 to bind and stabilize. In G‐box, specific stabilization is mediated by His/Lys9, Glu13, and Arg17. The Arg17 interacts with inner G base, and His/Lys9 interacts with the last G of the G‐box [61, 62]. The alpha‐helix function is involved in homo‐ and hetero‐dimerization and is formed by hydrophobic residues of isoleucine, leucine, and valine [34, 61]. Arabidopsis has been demonstrated that this residue is conserved in all bHLH proteins, indicating the importance of the basic region of the bHLH transcription factor in DNA binding [61, 63]. The second helix is involved in DNA binding through direct contact with the E‐box. Finally, the loop is responsible for the three‐dimensional arrangement of alpha‐helices, and residues from the first helix loop junction are involved in association with bHLH proteins [34, 61, 63, 64]. Basic helix‐loop‐helix transcription factors in plants are involved in processes such as flower development [65, 66], hormonal response [67, 68], metal homeostasis , and others. Regarding bHLH and their relation to flavonoid synthesis, the first bHLH involved in this pathway was detected in maize in 1989 . In this context, in
3.3. WDR proteins
Tryptophan‐aspartic acid repeat protein (WDR) or WD40 proteins are characterized by around 44–66 amino acids, delimited by the GH dipeptide on the N‐terminal size (11–24 residues from the N‐terminus) and the WD dipeptide on the C‐terminus [34, 77]. In Arabidopsis, WDR protein contains four (or more) tandem repeats composed of around 40 amino acids . In contrast to the majority of proteins, WDR is not involved in catalytic activities such as DNA binding or gene expression regulation, mostly acting as a platform due to its capacity to interact with more than one protein at the same time [34, 78]. The work of WDR involves eukaryotic cellular process such as cell division, vesicle formation, signal transduction, RNA processing, and transcription regulation . On the other hand, MYB and bHLH transcription factors have few WDR proteins involved in the flavonoid pathway, as shown in
3.4. MYB‐bHLH‐WDR (MBW complex)
MBW complex has been reported in Arabidopsis, petunia, and some varieties of grape [35, 82]. The most important function of these transcription factors is involved in the process related to DNA binding, activation of gene expression involved in the flavonoid pathway, and stabilization of the three‐dimensional configuration of the complex . Basic helix‐loop‐helix‐WDR interaction is needed to WDR protein translocation into the nucleus, and this was demonstrated in onion cells using green protein fluorescent (GPF), which when expressed alone is localized in the cytosol, whereas its co‐expression with PFWD and MYC‐RP enables the transport and localization in the nucleus . The AN11 from petunia showed the same results, being detected in the cytosol .
4. Antioxidant capacity of anthocyanins in berries and their use in human health
The radical scavenging activity (RSA) of anthocyanins is largely due to the presence of hydroxyl groups in position 3 of ring C and also in the 3', 4', and 5' positions in ring B of the molecule. In general, RSA of anthocyanidins (aglycons) is superior to their respective anthocyanins (glycosides), and this decreases when the number of sugar increases . Hanachi et al.  showed that fruits of
|Disease||Scientific name||Common name||Compound||Experimental conditions||Reference|
|Liver cancer||Strawberry||Crude extract|||
|Leukemia||Rosselle||Anthocyanin rich extract|||
|Gastric cancer||Black currant||Crude extract|||
|Colon caner||Bilberry||Anthocyanin‐rich extract|||
|Colon cancer||Chokeberry||Anthocyanin‐rich extract|||
|Colon cancer||Grape||Anthocyanin‐rich extract|||
|Esophagus cancer||Black raspberries||Anthocyanin‐rich extract|||
|Esophagus cancer||Black raspberries||Anthocyanins and ellagitannins|||
|Esophagus cancer||Red raspberries||Anthocyanins and ellagitannins|||
|Esophagus cancer||Strawberries||Anthocyanins and ellagitannins|||
|Esophagus cancer||Blueberries||Anthocyanins and ellagitannins|||
|Hepatic cancer||Barberries||Crude extract|||
|Liver cancer||Blueberries||Anthocyanin extract|||
|Liver cancer||Barberries||Crude extract|||
|Oral cancer||Black raspberries||Crude extract|||
|Skin cancer||Pomegranate||Crude extract||[92, 93]|
With respect to
5. Conclusions and future challenges
The potential use of anthocyanins from different plant species as natural compounds with a health benefit for humans opens a new trend for the prevention and alternative treatments of chronic diseases. Several reports have demonstrated that anthocyanins from berries could inhibit or decrease the growth of carcinogenic tumors by affecting cell proliferation, increasing or inhibiting enzymatic systems, and increasing expression of genes involved in cell protection. On the other hand, it is important to highlight that synthesis of anthocyanins in different tissues of plants species should be considered. In addition, the discovery and characterization of new regulatory elements of anthocyanin biosynthesis are crucial to understand and manipulate this pathway in breeding programs. Improving knowledge about increasing anthocyanin synthesis in crops of research and commercial interest, together with more animal and human model studies under
We are very grateful to PIA‐UFRO 16‐0006 and DI 16‐2013 projects from the Dirección de Investigación at the Universidad de La Frontera, Temuco, Chile.