Anthocyanin is a naturally occurring pigment in fruits and vegetables that gives them their vibrant red, purple or blue hues. It is an antioxidant belonging to the flavonoid family, and like other flavonoids, it has been shown to offer health benefits when ingested. It is thought to help lower oxidative stress, which in turn may reduce the risk of chronic conditions such as cancer, heart disease and diabetes.
Like many phytochemicals, anthocyanin is produced by plants to protect them from being eaten by predators and from environmental stressors, such as cold temperatures, drought or UV radiation. It can also improve plant resistance to disease and insects.
The chemistry of anthocyanin is based on the conjugation of two aromatic rings with a heterocyclic ring system. The color variation of anthocyanins relates to the structure of the A-ring, which can be influenced by substitution, methylation and glycosylation, as well as the distribution of positive charge on the B-ring. The A-rings of anthocyanins are generally phenolic, and the B-ring is an oxygenated heterocycle. The most common anthocyanins are cyanidin, delphinidin, malvidin, pelargonidin and peonidin (Fig. 24.1).
It is thought that the coloration of fruits and vegetables is due to the high concentrations of anthocyanins they contain. Anthocyanins are thought to act as an antioxidant by stabilizing other biomolecules in the body. Anthocyanins are also thought to provide a range of health benefits, including anti-inflammatory, anticancer, anti-diabetic and anti-obesity properties.
In one study, anthocyanins reduced the number of aberrant crypt foci and colonic cell proliferation in rats, while decreasing the expression of inflammatory cytokines and COX-2 in colon cells. Anthocyanins also stimulated AMP-activated protein kinase and lowered triglyceride levels in diabetic nephropathy mice.
A diet rich in anthocyanins can also aid in weight loss. This is thought to be a result of the fact that they tend to reduce the amount of lipids absorbed by the digestive tract, which in turn leads to decreased fat storage. In addition, anthocyanins can stimulate metabolism by upregulating AMPK and acetyl-CoA carboxylase.
In a recent study, black rice anthocyanins were found to suppress metastasis in breast cancer cells in vitro and in vivo. They inhibited RAS/RAF/MAPK (retrovirus-associated DNA sequences/rapidly accelerated fibrosarcoma/mitogen-activated protein kinase) signaling in MDA-MB-453 cells, as well as inhibited phosphorylation of ERK and JNK, and downregulated secretion of matrix metalloproteinases 2 and 9. In vivo, anthocyanins increased AMPK activity, lowered insulin resistance and glycemic load, and improved vascular reactivity in diabetes mellitus patients. In addition, they prevented the development of oxidative damage and vascular endothelial dysfunction in diabetic mice.