Alcoholic purine bases
- Published: Aug 3, 2009
- Author: Steve Down
- Channels: HPLC
Many of us like the odd tipple and can manage our drinking habits so that there are minimal affects on our health, which is just as well. Apart from alcoholism, anti-social behaviour and the risks associated with being drunk, excess alcohol intake is linked with a number of conditions including liver cirrhosis, stomach ulcers, heart attacks and even cancer. It has also been implicated in the onset of hyperuricaemia and gout.
Hyperuricaemia, as the name implies, is the build up of excess amounts of uric acid in the blood. Under normal circumstances, this does not require medical attention but sustained hyperuricaemia is the primary risk factor for gout. When there is too much uric acid for the kidneys to cope with, some remains in the blood and can crystallise around the joints, hence gout.
The link between uric acid and alcohol is the purine bases adenine, guanine, xanthine and hypoxanthine. Once imbibed, they are metabolised to uric acid in an enzymatic process involving xanthine oxidase. So, reduced intake of foods that are high in purines will, in turn, reduce the level of purines in the body.
Although there are pharmacological treatments for gout, there have also been recent moves to attend to this condition by lifestyle guidance. For the case of alcoholic drinks, that means reducing intake or moving to low-purine options. In Japan, researchers from Teikyo University, Tokyo, have carried out some of the groundwork by analysing the purine contents of a range of drinks using HPLC.
Kiyoko Kaneko, Tomoyo Yamanobe and Shin Fujimori used a multimode column containing anion exchange and reversed-phase material. This was selected over a reversed-phase column due to published reports of low retention and poor resolution from coexisting compounds. Acidic sodium phosphate buffer was employed as the mobile phase with a UV detector.
Under these conditions, the four purine bases and uric acid were well-separated, eluting within 40 minutes. The detection limits were 5.0 ng for xanthine and 2.5 ng for the others and the calibration curves were linear over 2.5-200 ng. The precision and accuracy values were also deemed satisfactory.
The method was applied to the purine contents of spirits (whisky, brandy, shochu), wine, beer (regular, local, low-malt, low alcohol and low-malt/low purine types), Chinese shoko-shu, ume liquor and a beer-flavoured beverage. Freeze-dried samples were oxidised with strong perchloric acid to convert nucleic acids, nucleosides and nucleotides to the corresponding purine bases.
The resulting solutions were analysed on a multimode column containing anion exchange and reversed-phase material. This was selected over a reversed-phase column due to published reports of low retention and poor resolution from coexisting compounds. Acidic sodium phosphate buffer was employed as the mobile phase.
The presence of other compounds in the extracts complicated identification of the purines in the chromatograms from the real samples, so Kaneko introduced an enzymatic peak shift treatment. The extracts were oxidised with xanthine oxidase which targets adenine, guanine, xanthine and hypoxanthine. A second treatment with guanase converts guanine to xanthine. The peak areas of the target purines were calculated from the differences in peak areas before and after enzyme treatment.
The xanthine oxidase and guanase reactions took 180 and 60 minutes, respectively, which has a marked effect on the overall analysis duration. However, the team preferred to use them because they are "more accurate for quantitative purine analysis in materials such as food and beverages, which contain numerous additional materials."
The total purine contents of the beverage studied were largest for local beers and some low-alcohol beers, with values greater than 800 µM. Some of them had contents 2.5-fold greater than regular beers.
However, low-malt beers contained less and the low malt/low purine beer had about 2-6% of the purines in regular beer. Levels in wine and Japanese sake were 28-110 µM with whisky and shochu at 0.3-10.6 µM. Beer-flavoured beverages also displayed reduced total purine contents at 70-160 µM.
The major purine bases differed from drink to drink. Guanine was dominant in beer whereas hypoxanthine dominated in Chinese liquor.
The data show the great disparity in purine contents across different alcoholic beverages available in Japan and can be used by physicians to direct gout patients towards a more suitable tipple. Management of the condition by considered beverage selection could alleviate the symptoms and negate the need for medication.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.