Cancer Letters

Cancer Letters

Volume 269, Issue 2, 8 October 2008, Pages 281-290
Cancer Letters

Mini-review
Anthocyanins and their role in cancer prevention

https://doi.org/10.1016/j.canlet.2008.05.020Get rights and content

Abstract

Anthocyanins are the most abundant flavonoid constituents of fruits and vegetables. The conjugated bonds in their structures, which absorb light at about 500 nm, are the basis for the bright red, blue and purple colors of fruits and vegetables, as well as the autumn foliage of deciduous trees. The daily intake of anthocyanins in residents of the United States is estimated to be about 200 mg or about 9-fold higher than that of other dietary flavonoids. In this review, we summarize the latest developments on the anti-carcinogenic activities of anthocyanins and anthocyanin-rich extracts in cell culture models and in animal model tumor systems, and discuss their molecular mechanisms of action. We also suggest reasons for the apparent lack of correlation between the effectiveness of anthocyanins in laboratory model systems and in humans as evidenced by epidemiological studies. Future studies aimed at enhancing the absorption of anthocyanins and/or their metabolites are likely to be necessary for their ultimate use for chemoprevention of human cancer.

Introduction

Anthocyanins occur ubiquitously in the plant kingdom and confer the bright red, blue and purple colors to fruits and vegetables such as berries, grapes, apples, purple cabbage and corn. Of potential importance to human health is the relatively high concentration of anthocyanins in the diet. The daily intake of anthocyanins in the U.S. diet is estimated to be between 180 and 215 mg whereas, the intake of other dietary flavonoids such as genistein, quercetin and apigenin is only 20–25 mg/day [1]. Epidemiologic studies suggest that the consumption of anthocyanins lowers the risk of cardiovascular disease, diabetes, arthritis and cancer due, at least in part, to their anti-oxidant and anti-inflammatory activities [2].

In the present review, we highlight recent studies on the cancer preventative activities of the anthocyanins, including results from in vitro cell culture and in vivo animal model tumor systems, as well as data from human epidemiological studies. Although laboratory studies have provided some clues on the molecular mechanism(s) by which anthocyanins inhibit carcinogenesis, there is still much to be learned. In addition, the relevance of the in vitro studies to the in vivo situation needs to be confirmed in view of the high concentrations of anthocyanins employed in the in vitro studies.

Section snippets

Chemistry of anthocyanins

Anthocyanins occur naturally in fruits and vegetables as glycosides, having glucose, galactose, rhamnose, xylose or arabinose attached to an aglycon nucleus [3], [4]. In contrast to other flavonoids, the anthocyanins carry a positive charge in acidic solution [3]. They are water-soluble and, depending upon pH and the presence of chelating metal ions, are intensely colored in blue, purple, or red. The de-glycosylated or aglycone forms of anthocyanins are known as anthocyanidins (Fig. 1). The six

Antioxidant effects

The phenolic structure of anthocyanins is responsible for their antioxidant activity; i.e., ability to scavenge reactive oxygen species (ROS) such as superoxide (O2.-), singlet oxygen (‘O2), peroxide (ROO), hydrogen peroxide (H2O2), and hydroxyl radical (OHradical dot) [5]. The antioxidant effects of anthocyanins in vitro have been demonstrated using several cell culture systems including colon [6], [7], endothelial [8], liver [9], [10], breast [11], [12] and leukemic cells [13], and keratinocytes [14].

Pharmacokinetics and metabolism of anthocyanins

The bioavailability, pharmacokinetics of distribution, and metabolism of anthocyanins in animals and in humans have been summarized in a recent review [60]. 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 [60], [61]. We investigated the absorption and metabolism of black raspberry anthocyanins in humans when administered orally at high doses

Conclusions

Anthocyanins have been shown to exhibit anti-carcinogenic activity against multiple cancer cell types in vitro and tumor types in vivo. Potential cancer chemopreventive activities of anthocyanins revealed from in vitro studies include radical scavenging activity, stimulation of phase II detoxifying enzymes, reduced cell proliferation, inflammation, angiogenesis and invasiveness, and induction of apoptosis and differentiation. The anthocyanins modulate the expression and activation of multiple

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