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Protective properties of coffee

Researchers across the globe have been using the comet assay to investigate the protective properties of coffee. Coffee is one of the most popular and widely consumed beverages worldwide.

Study 1

European researchers investigated the effect of coffee in relation to liver damage (in particular pre-neoplastic hepatic foci) and DNA damage.  The impact of drinking coffee samples on DNA damage was quantified by the comet assay.  In addition, comet assay experiments were conducted with pure caffeine.

The consumption of coffee reduced the frequencies of hepatic foci and DNA migration was reduced between 65 and 75% with the caffeine containing coffee samples.  DNA migration (% DNA in tail) was determined with a computer-aided comet assay image analysis system (Comet Assay IV, Perceptive Instruments, UK). The experiments were carried out according to the international guidelines for single cell gel electrophoresis experiments. 

In additional experiments, the researchers found clear protective effects with caffeine at dose levels corresponding to those contained in the coffee.

To read about this study in more detail, including the authors’ hypothesis that the induction of UDP-glucuronosyltransferase contributes to the chemopreventive effects of coffee, and experimental details of the AFB1-induced DNA damage method used, please refer to the full publication (Protective effects of coffee against induction of DNA damage and pre-neoplastic foci by aflatoxin B1)

Study 2

Another group of researchers looked at spent coffee.  Previous studies have shown that spent coffee is a good source of antioxidants.  Cells from a human derived cell line (HeLa) were incubated with spent coffee extracts for both 2 hour and 24 hour exposures. 

The viability of cells was not affected by the incubations, but the amount of DNA damage (induced by H2O2) was decreased significantly when the cells were incubated with spent coffee extracts.  A total of 100 comets on each slide were scored through a computer-assisted image analysis (Comet Assay IV, Perceptive Instruments), by measuring the percentage of DNA in the tail.

Two types of coffee extract were used in this investigation: Arabica filter and Robusta espresso.  The researchers concluded that the Robusta spent coffee extract had a higher effectiveness.  They hypothesised that this might be due to antioxidant compounds, such as caffeine and other Maillard reaction products, because the Robusta extract contained less caffeoylquinic acids and melanoidins.  This work suggested the potential antioxidant and genoprotective properties of spent coffee in human cells. (The publication can be accessed here: Antioxidant and genoprotective effects of spent coffee extracts in human cells)

Study 3  

The authors of “Coffee and Coffee Compounds are Effective Antioxidents in Human Cells and In Vivo” (a book section found in: Risk Assessment of Phytochemicals in Food: Novel Approaches) have written about the epidemiological studies which suggest that coffee can reduce the risk of degenerative diseases such as type 2 diabetes, cardiovascular disease and cancer.  These beneficial effects have been attributed to the antioxidant activity of coffee brew, a complex mixture of bioactive compounds.

The researchers studied the direct antioxidant capacity of coffee constituents and extracts and their potential to reduce DNA damage.  A cell free system and a Caco-2 cell line were both used in the investigation.  The comet assay was performed on the Caco-2 cells. Comet analysis was performed with a system from Perceptive Instruments and 2 x 50 comets were scored per slide.  DNA damage was expressed as relative tail intensity. 

Menadione-induced DNA damage in Caco-2 cells was reduced by N-methyl-(2-methyl)-pyridinium ion and slightly diminished by N-methylepyridinium ion.  In healthy probands, oxidative DNA damage in blood was reduced by coffee brews.  The results suggested that N-methylpyridinium compounds contribute to the antioxidative activity of coffee in human cells.   For full interpretation of the results, please refer to the original publication (Risk Assessment of Phytochemicals in Food: Novel Approaches ISBN: 978-3-527-32929-8, Dec 2010)