Folic Acid

NEWS FROM THE ROYAL SOCIETY OF CHEMISTRY'S ANNUAL MEETING

David Bradley reports from Edinburgh (U.K.).

Folate assay fails Countless folate assays are giving inaccurate readings because of the way they are de­signed, according to Tony Wright of the In­stitute of Food Research (Norwich, U.K.). Results underestimate the actual folate level, which Wright says may cause significant problems in developing "robust relation­ships between folate status and dis­ease", affect quality assessment schemes for clinical and nonclini­cal laboratories, and skew epide­miological monitoring of health indicators.

Folates are derivatives of folic acid, a water-solu­ble B vitamin crucial to more than 100 bio­chemical processes, such as the synthesis of amino acids and DNA bases. Wright points out there is firm evidence that adequate folate intake before pregnancy prevents most neu­ral tube defects, including spina bifida. Defi­ciency has also been implicated in vascular disease, DNA repair problems leading to cancer and impaired immunity.

The standard measure of folate levels, or "status", is carried out on red blood cells

in the red cell folate assay using either a microbiological assay or a radio folate bind­ing protein assay, which, Wright says, have been considered "simple" since the late 1950s. "The analysis provides an indicator of deficiency risk in women of child-bearing age

and the general population," he explains. However, Wright and his colleagues have assessed these simple techniques and found a large variation between and within each assay type.

Delving deeper into the technicalities, the team uncovered numerous assump­tions that do not hold up to close scrutiny.

For example, the venous blood samples are usually incubated for 30 min at body temper­ature with a hypotonic hemolyzing solution to split the red cells, and an enzyme is added

fo deconjugate the naturally occur­ring folate polyglutamate to folate

monoglutamate—the assayable form. By this time, the assay-able folate level has plateaued. The problem, says Wright, is that the plateau represents

only the level of folate al­lowed access to the de-

conjugase enzyme. It does not take into ac­count the potential

binding of folate to he­moglobin nor the degree

of oxygenation of the he­moglobin in the sample,

which, he suggests, can result in folate trapped within the cavity of oxyhe­

moglobin and a false low reading.

There are other problems. Wright says sampled blood can be up to 75% oxygen­ated, which can, in theory, lead to a 4-fold underestimation of a person's folate status. He suggests that the folate assays need to be reinvented so that full deconjugation of any folate present can take place. "Suffocat­ing" the samples to expel oxygen might be a solution.

GM check New broad-ranging analytical techniques that make no assumptions about what is dangerous could help in improving risk assessment of genetically modified (GM) crops, claims Andrew Chesson, who stud­ies the effects of GM plants on the human digestive tract at the Rowett Research In­stitute (Aberdeen, U.K.). Chesson believes established methods have one major short­fall in that they all rely on some knowledge of the suspect materials being tested. This, he says, means they cannot provide a suffi­cient safety check for the health effects on humans and animals nor the environmen­tal impact of GM organisms

One of the main problems faced in the risk assessment of GM crops is that, while the levels of known hazardous chemicals produced in a plant geneti­cally engineered for insect resistance are relatively simple to test for, any un­

expected chemicals go unchecked when using chromatographic or spectroscopic techniques. Crops meant for agricultural use rather than human consumption, such as oilseed rape, much of which is fed to pigs and sheep, could allow hazardous com­pounds to enter the food chain insidiously.

This issue of GM food is of particular concern in Europe. One of the researchers at the Rowett Research Institute, Arpad Pusztai, announced results that he claimed demonstrated certain plant lectins being engineered into potatoes caused adverse gut reactions in rats. Pusztai was eventually forced out of his position when attempts to repeat his experiments did not bear up to scientific scrutiny.

However, the media outcry and public response are still raging in the United King­dom, with food manufacturers, restauran-teurs, and other suppliers doing their best to distance their menus from anything GM.

Nevertheless, Chesson predicts mat the number of GM crop trials is likely to in­crease rapidly over the next few years irrespective of public and activist pres­sure. The benefits perceived by the food industry are just too high, and the num­ber of products seeking approval will rise in parallel. "It is essential that analytical tools to assess these products keep pace with the developments," says Chesson.

Techniques such as proteomics and DNA-array microchips might be used to test for equivalence between conven­tional and GM crops so that risks asso­ciated with unknowns could be ex­cluded, although these approaches are yet to be assessed. Other scientists strongly disagree with Chesson's idea that current safety evaluation of GM organisms is flawed because new ap­proaches have not yet been integrated into the test procedures.

Analytical Chemistry News & Features, November 1, 1999 729 A