Ribes nigrum and ribes rubrum, two examples of fruit that contains anthocyanins
Anthocyanins (from Greek: anthos = flower + kyanos = blue) are pigments that belong to the class of flavonoids. In plants they have two functions: 1) they confers the colors which attract pollinators and 2) act as a sunscreen, protecting cells from high-light damage by absorbing UV light. Studies demonstrates that these flavonoids can be involved in cancer prevention and help to protect from age-related macular degeneration (AMD). Age-related macular degeneration is one of the leading causes of blindness in the developed world. Anthocyanins’ antioxidant proprieties helps to reduce risk of AMD, and improves night vision.
The phenolic structure of anthocyanins is responsible for their antioxidant activity: they can scavenge reactive oxygen species (ROS) and increase the oxygen-radical absorbing capacity of cells. This antioxidant activity reduce lipid peroxidation and protects DNA from mutagenesis. Although most of the protective effects of anthocyanins are attributed to their ability to scavenge ROS, they also function by stimulating the expression of Phase II detoxification enzymes, by chelating metals and by direct binding to proteins.
General structure of anthocyanins
Inflammation has been shown to play a role in the promotion of some types of cancer in animals. Abnormal up-regulation of two inflammatory proteins, NF-κB and cyclooxygenase-2 (COX-2), is a common occurrence in many cancers. Anthocyanins suppress inflammatory response through targeting the phospholipase A2 and PI3K/Akt and NF-κB pathways.
Angiogenesis is the process of forming new blood vessels from the existing vascular network, and is an important factor in tumor growth. Some of the most potent angiogenesis-activating molecules are members of a family of vascular endothelial growth factors (VEGF), and VEGF expression is frequently enhanced in developing tumors. Anthocyanins have been shown to suppress angiogenesis through several mechanisms such as: inhibition of H2O2- and tumor necrosis factor alpha (TNF-α)-induced VEGF expression in epidermal keratinocytes, and by reducing VEGF and VEGF receptor expression in endothelial cells
Degradation of the basement membrane collagen by proteolysis is an early and critical invasion event. Tumor and stromal cells have to secrete proteolytic enzymes to facilitate degradation of the extracellular matrix barriers for successful tumor cell intravasation. Degradation of the basement membrane doesn’t depend only on the amount of proteolytic enzymes present but on the balance of activated proteases and their inhibitors. Anthocyanin extracts have been evaluated for their ability to inhibit the invasion of multiple cancer cell types through reducing the expression of MMP which degrade extracellular matrix.
In vitro was shown the anthocyanins ability to block various stages of the cell cycle via effects on cell cycle regulator proteins (e.g., p53, p21, p27, etc.). Several investigations have compared the anthocyanins’ antiproliferative effects on normal cells vs. cancer cells and found that they selectively inhibit the growth of cancer cells with relatively little or no effect on the growth of normal cells. The mechanisms for the anthocyanins selective effect on the growth of cancer cells vs. normal cells are not known yet.
Induction of apoptosis
Apoptosis, or programmed cell death, plays a key role in the development and growth regulation of normal cells, and is often dysregulated in cancer cells. Some of the most effective chemopreventive agents act in cancer cells as strong inducers of apoptosis. in vitro, anthocyanin-rich extracts from berries and grapes, and several pure anthocyanins, have exhibited pro-apoptotic effects in many cell types. They can induce apoptosis through:
- intrinsic (mitochondrial) pathway: anthocyanin treatment of cancer cells results in an increase the release of cytochrome C and of modulation of caspase-dependent anti- and pro-apoptotic proteins;
- extrinsic (FAS) pathway: anthocyanins modulate the expression of FAS and FAS ligand in cancer cells which brings to apoptosis.
Besides, the treatment with anthocyanins leads to an accumulation of ROS and subsequent apoptosis in cancer cells, but not in normal ones. This suggests that the ROS-mediated mitochondrial caspase-independent pathway is an important factor for anthocyanin-induced apoptosis.
Anthocyanins have been shown to inhibit the development of cancer in carcinogen-treated animals and in animals with a hereditary predisposition to these diseases. In a pre-surgical model, 25 colon cancer patients that had not received prior therapy consumed 60g/day (20g, 3 times/day) of black raspberry powder for 2–4 weeks. Biopsies of tissues were taken before and after berry treatment. The berries reduced proliferation rates and increased apoptosis in colon tumors but not in normal-appearing crypts. The number of stained blood vessels was also reduced in berry-treated colon tumors. This suggests an anti-angiogenic effect of the short-term berry treatment. The berries anthocyanins contribution to these effects is under investigation.
In general, in both animals and humans, the anthocyanins are absorbed as intact glycosides, and their absorption and elimination is rapid. However, the efficiency of their absorption is relatively poor. Anthocyanins have been shown to inhibit malignant cell growth, to stimulate apoptosis and to modulate oncogenic signaling events in vitro in the 10−6 to 10−4 M concentration range. Studies about the uptake of anthocyanins in humans after their consumption as mixtures have shown that they reach levels of 10−8 to 10−7 M in human blood and suggested that they may have little efficacy in tissues other than the G.I. tract and skin, where they can be absorbed locally.
Anthocyanins and their role in cancer prevention, 2008
The molecular basis for the pharmacological activity of anthocyans
Prevention of age-related macular degeneration