Caffeine stacks up against cancer: UV-Vis reveals mechanism

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  • Published: Feb 1, 2011
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Caffeine stacks up against cancer: UV-Vis reveals mechanism

Caffeinated carcinogens

Methylxanthine alkaloids, such as caffeine, have been implicated as a risk factor in several forms of cancer. Now, UV-vis spectroscopy and other techniques have been used to reveal a possible mechanism that demonstrates they may have the opposite activity - protecting us from aromatic mutagens and carcinogens by stacking up and blocking their detrimental activity.

Anna Woziwodzka and Jacek Piosik of the Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology UG and MUG, in Gdansk, Poland and Anna Gwizdek-Wisniewska of the centre's Department of Biotechnology explain how caffeine is the most widely used and well known of the methylxanthine (MTX) alkaloids. It is present in various plants where it acts as a natural pesticide, paralysing and killing insects that try to feed on the plant. It is best known for its stimulating properties in coffee and tea and so-called energy drinks.

However, as with many natural products, caffeine does have a dark side. There is some statistical evidence to indicate that it may have carcinogenic properties. That said there are no definitive studies that support this conjecture. Indeed, caffeine may actually have a protective effect against ingested carcinogens, because it can form direct non-covalent interactions with many aromatic amines through a pi-pi stacking process.

Cooking up problems

Heterocyclic aromatic amines are formed when meat and fish are cooked at temperatures above 150 Celsius. They are also present at lower concentrations in sewage, exhaust fumes, cigarette smoke, river and rain water and as atmospheric pollutants. A person's daily intake is low at just 0.4 to 16 micrograms per person but they are strongly mutagenic, especially after cytochrome P450 metabolic activation. They have been shown to be carcinogens in laboratory animal tests. They are also implicated in breast, colorectal, pancreatic and urothelial cancer in people with a diet high in meat products. Of course, given their origins in common foods it would be very difficult to eliminate them from the diet of many people without significant lifestyle changes.

Growing evidence suggested that caffeine and other MTX compounds, including theophylline (found in chocolate) and the drug pentoxifylline (Trental, used to treat sickle-cell anaemia, obstructed arteries and vascular dementia), may ameliorate the carcinogenic activity of heterocyclic aromatic amines. The standard Ames test (Salmonella typhimurium TA98 strain) and the Vibrio harveyi A16 strain bioluminescence assay on these compounds demonstrates that they do indeed reduce activity in the carcinogens. Now, the researchers have used UV-Vis spectroscopy, calculations based on a thermodynamic model of mixed aggregation and titration microcalorimetry to probe a possible mechanism for this effect.

Chemical protection

Their data show that MTX compounds form stacking complexes with carcinogenic imidazoquinoline-type (IQ-type) food-borne heterocyclic aromatic amines. Estimated association constants are in a range to support the formation of such complexes in both neutral and acidic environments. A similar phenomenon is observed with chlorophyllin, which is present in green leafy vegetables and is thought to be a "carcinogenic interceptor" molecule protecting against polycyclic aromatic hydrocarbons and the mould compound aflatoxin B1 as well as heterocyclic aromatic amines. There are apparently many benefits to a diet rich in leafy, green vegetables and indeed in having plenty of fresh fruit in your diet and in reducing your total meat intake. Whether or not the benefits of caffeine as a putative carcinogenic interceptor would outweigh any health risks associated with this stimulant remain to be seen. However, now a plausible chemical mechanism has been demonstrated for a possible protective effect so that future studies might bear in mind this possibility.

Piosik points out that recommendations regarding caffeine and its consumption are complex and depend on several conditions, such as personal health, personal disposition to cancer and other diseases (gastric diseases, blood pressure problems etc.) as well as personal tolerance to caffeine doses. "The human diet includes many contaminants, which are mutagens and carcinogens (heterocyclic aromatic amines, polycyclic aromatic hydrocarbons etc.) as well as many compounds, which have protective ability against cancer (interceptor molecules)," he explains. "Elimination of all possible mutagenic contaminants from the human diet is unlikely or even impossible. Therefore, the influence of several food elements on human health is the result of its concentration in food and personal disposition." He adds that the "protective effects of caffeine predominate over its negative action. I personally like to drink coffee and beverages containing caffeine, but anticancer caffeine action is still speculation and required further detailed studies."

 

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Methylxanthine alkaloids, such as caffeine, have been implicated as a risk factor in several forms of cancer. Now, UV-vis spectroscopy and other techniques have been used to reveal a possible mechanism that demonstrates they may have the opposite activity - protecting us from aromatic mutagens and carcinogens by stacking up and blocking their detrimental activity.

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