February 7, 2019 — Aspartame is one of the most studied ingredients in our food supply, but it is also one of the most controversial. Recently, new safety studies on aspartame were assessed in the publication “Mutagenicity and genotoxicity studies of aspartame,” which recently appeared in Regulatory Toxicology and Pharmacology. So what are these studies? Why were they conducted? And what do they tell us?
What are these studies?
An important part of the extensive toxicological testing conducted to determine whether or not a food additive is safe for human consumption involves testing for its potential to cause genetic damage. Such effects are known to lead to possible hereditary effects or cancer, and standard tests are required to examine the ability of a substance to induce genetic changes, such as mutations or changes in the DNA. Therefore, it’s not surprising that extensive genetic toxicology testing of aspartame was required and conducted prior to its approval as a food additive.
For regulatory agencies to consider and accept results from standard studies, they must follow strict internationally accepted protocols and be conducted under experimental conditions that conform to what is known as Good Laboratory Practice (GLP). Studies conducted using the standard protocols at that time consistently demonstrated that aspartame did not cause any genetic damage (see review by Magnuson et al., 2007).
Why were new studies conducted?
The early studies conducted to support the approval of aspartame now do not completely comply with modern guidelines and were not published in detail in the open scientific literature. Since the approval of aspartame in 1981, other researchers have conducted studies with aspartame, using various different methods and assays, which do not meet the criteria described above. Further, these studies have reported conflicting results. Despite the apparent limitations and lack of recognition of the validity of the methods used, these reports have spurred on questions regarding the safety of aspartame. Thus, the purpose of the studies conducted by Otabe et al (2018) was to re-assess aspartame with the most current internationally-established guideline protocols in GLP-compliant laboratories.
How do these assays test for genetic toxicity?
The most common assay required by regulatory authorities for detection of mutation is the standard Ames test. Developed in the laboratory of renowned biochemist specializing in cancer researcher, Bruce Ames (University of California), strains of Salmonella bacteria have unique features that promote sensitivity to test chemicals. For example, their cell walls have increased permeability to allow easier access of chemical agents to the cells’ DNA, and they are deficient in DNA repair enzymes (which are normally also present in all human cells) so that damage to DNA is not fixed but can lead directly to mutation. In addition, certain bacterial strains contain an extra genetic element that makes the cells more responsive to chemical mutagens. The current, most accepted version of the Ames test also includes a bacterial strain using a repair-deficient variant of the bacterium E. coli. The sensitivity of the Ames test is further enhanced by inclusion of an extract of mammalian enzymes for metabolic activation. The purpose of this extract is to mimic normal mammalian metabolism in vitro so that the assay can detect chemical compounds that may not be directly mutagenic, but whose metabolites are mutagenic when activated through metabolism enzymes. The Otabe study tested aspartame (99.5% pure) in five standard Salmonella and E. coli strains. The results of this GLP research showed that aspartame has no mutagenic potential in this assay.
In addition to such tests involving direct treatment of cultured cells (i.e., in vitro), a genetic test using whole animals (i.e., in vivo) is also required. The standard in vivo assay used to detect genetic changes in chromosomes is the mouse bone marrow micronucleus assay. The relevance of an in vivo system to the intended human consumption of a food substance starts with oral administration, followed by all the important bodily functions involved in absorption, distribution, metabolism and excretion. Bone marrow is the site of actively dividing blood cells that are sensitive to DNA damaging agents that can cause structural or numerical chromosome aberrations. These result in chromosome fragments that can be visualized in daughter blood cells as micronuclei in comparison to normal nuclei. In the Otabe study, mice were treated with aspartame according to internationally recognized protocols. The results showed conclusively that aspartame does not cause chromosomal damage in mouse bone marrow cells.
What do these new studies tell us?
The results from GLP-compliant studies using the most current and well-accepted protocols show conclusively that aspartame does not cause genetic effects (i.e., aspartame is non-mutagenic and non-genotoxic). These results support the findings of the initial studies conducted to support the registrations of aspartame, and further confirm that aspartame and aspartame-sweetened products are safe to consume.