Safety of Genetically Engineered Foods Approaches to Assessing Unintended Health Effects (2004) / Chapter Skim
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4 New Approaches for Identifying Unintened Changes in Food Composition
4 New Approaches for Identifying Unintened Changes in Food Composition
Pages 73-102
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From page 73... ...
It is this comparative approach that is perhaps the most important in the safety evaluation of new food items derived from all means of genetic modification, including conventional breeding techniques, mutagenesis techniques, or genetic engineering (see Operational Definitions in Chapter 1)
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From page 74... ...
foods. Advanced molecular genetic, proteomic, and metabolite profiling techniques are rapidly developing technologies that have the potential to provide an enormous amount of data for a given organism, tissue, or food product.
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TARGETED QUANTITATIVE ANALYSIS VERSUS PROFILING METHODS Two basic analytical approaches exist, and each has merit in certain applications. Targeted quantitative analysis is the traditional approach in which a method is established to quantify a predefined compound or class of compounds (e.g., amino acids, lipids, vitamins, or RNAs for specific genes)
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From page 76... ...
Selected examples of both targeted analysis and profiling methods, which illustrate the advantages and current limitations, are discussed below. General Considerations for Accuracy, Reproducibility, and Artifacts in Analysis of Food and Other Biological Material Important characteristics of any analytical technique are the precision and accuracy of the chosen method, the robustness and reproducibility of the method within and between laboratories, and the ongoing identification and appreciation of any potential sources of artifacts in the methods employed.
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For targeted analyses (e.g., particular vitamins or amino acids) technical variation and artifacts can often be minimized as only a limited number of compounds of often similar chemistry are being targeted and analyzed.
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, essential macronutrients (essential amino acids and fatty acids) , nonessential nutrients of importance to health (e.g., dietary fiber, total fat)
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From page 79... ...
In addition, increasing the concentration of a chemical compound, such as a vitamin or other phytochemical, could lead to an increased concentration of catabolic products. While these examples may or may not be relevant to food safety, they illustrate several ways in which unexpected compositional changes could occur.
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From page 80... ...
Genetically induced changes in protein expression could either lessen or accentuate these nutritional limitations, as could changes in the biosynthesis of the essential amino acids. Fatty Acids.
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From page 81... ...
and LC-MS methods are well suited for such a separation and quantitative analysis of these oligosaccharides. Food Constituents that Potentially Affect Nutrient Bioavailability Although the concept of nutrient bioavailability is very complex, several factors that affect bioavailability are sufficiently well-characterized to merit their inclusion in a targeted analysis of relevant food.
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From page 82... ...
Contemporary HPLC, GC, LC-MS, and GC-MS methods facilitate rapid and sensitive targeted analyses of specific alkaloids. Targeted Analysis of DNA, RNA, and Proteins To provide a complete picture of the genetic and compositional changes of food produced by either genetic engineering or conventional breeding, a targeted analysis using the tools of modern molecular biology should be used to provide information regarding the specific genetic changes that have occurred.
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From page 83... ...
Perhaps most important in a food safety assessment is the measurement of the expression of the protein encoded by the transgene and, if enzymatically active, the concentration of the reaction products and their metabolites, as discussed above. Information on approaches to safety assessment of GM foods is also available in the Report of the Fourth Session of the Codex Ad Hoc Intergovernmental Task Force on Foods Derived from Biotechnology (FAO/WHO, 2003)
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From page 84... ...
Such analytical improvements also have led to a better ability to detect and quantify compositional changes associated with biological variation and with variables such as agricultural practices, climate, and genetics. In addition, the application of such techniques has led to the recognition that the composition of biological material, especially plants, is far more complex and variable than previously believed, and that the majority of plant chemical constituents have yet to be identified and structurally characterized.
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From page 85... ...
The technical variation of most GC-MS methodologies is generally less than 10 percent, while the biological variation encountered in several comprehensive studies averages 50 percent and is highly dependent on the particular compound in question (Fiehn et al., 2000b; Roessner et al., 2000)
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From page 86... ...
Technical variation in these studies was less than 10 percent, while biological variation for 11 compounds studied in detail ranged from 17 to 56 percent, with an average of approximately 40 percent. Two mutants derived from chemical mutagenesis were compared with their respective wild-type parental lines (Fiehn et al., 2000a)
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Approximately 30 to 40 percent of the metabolites of a leaf were significantly different from the overall average leaf profile. These data highlight the resolution that can be obtained with metabolite profiling, but they also raise issues of the natural biological variation that exists when tissues are considered for sampling.
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From page 88... ...
Analysis of various extracts can identify the intermediates and products of metabolism and, if done sequentially over time, rates of reactions can be determined. While this does not provide information regarding composition, which is the primary analytical goal in a food safety assessment, such techniques do provide a means of assessing metabolic changes that might be introduced by genetic engineering, mutagenesis, or conventional breeding.
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From page 89... ...
, it is inappropriate for identifying unintended effects of genetic modification because there is no attempt to determine the specific chemical nature of the compositional change identified, only that one sample is different from another. One particular approach that has great potential in identifying possible unintended effects of genetic modification is based on comparison with baseline metabolic profiles.
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From page 90... ...
It is very difficult to interpret or predict the effects on human health of changes in the composition of a single food item and, especially, the health effects of changes in a single food item present in the total diet. This is true even for compounds for which large amounts of nutritional data are already known (e.g., specific amino acids or fatty acids; see Chapter 6)
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Pattern Recognition Methods for Evaluation of Compositional Equivalence The profiling methods described above are useful analytical tools for unique compounds. However, they have limitations when applied to complex mixtures, such as food.
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Although targeted analyses are fully adequate for the determination of individual elements of nutritional and toxicological interest, analytical approaches that allow a determination of multielement profiles have conceptual and practical advantages for monitoring the composition of GM food products. Nontargeted mineral analysis is performed typically using either inductively coupled plasma-optical emission spectrometry or inductively coupled plasmamass spectrometry, with thermal ionization mass spectrometry as an alternative
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From page 93... ...
As with other aspects of the profiling of food constituents, the interpretation of data from multielement analysis is the critical issue in evaluating differences due to genetic modification in the context of compositional effects of geographic location, climate, and agronomic variables. GENOMICS It has been proposed that differential gene expression be used as a method to determine the substantial equivalence of genetically modified organisms (GMOs)
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Proteins are extremely important biochemical components as they are very abundant in all biological material, and they are the molecular machines that function in cells. They are made up of linear chains of any of 21 individual amino acid units (plus a few more very rare amino acids)
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can frequently be determined by further analysis of a partial amino acid sequence obtained by chemical or MS analysis. MS analysis of proteins (e.g., from 2-D gel electrophoresis)
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This method consists of breaking the proteins in each gel spot with a single endoprotease enzyme that cuts the sequence of amino acids at well-known positions, resulting in a mixture of smaller peptides. The peptide mixture is then injected into a mass spectrometer; usually a matrix-assisted laser desorption/ionisation-time of flight mass spectrometry instrument, which can accurately measure the mass of the peptides (down to fractions of atomic units)
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From page 97... ...
Thus the reference sequence database should include all known proteins and be kept up to date. Usually the databases used in proteomic analysis are the Swiss-Prot (a database with high-quality annotation)
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From page 98... ...
can be incorporated into targeted analysis independent of a proteomic analysis. INFORMATION OBTAINED FROM NEW ANALYTICAL TECHNIQUES With the increased sensitivity and resolution of technology during the past decade, an analyst now has the ability to detect and quantify tens of thousands of possible changes in biological molecules (e.g., DNA, RNA, protein, and metabolites)
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DISCUSSION Regardless of the analytical methods used and the quality and depth of compositional data obtained, data interpretation remains the critical issue for evaluating the significance of unintended compositional changes. Questions that bear consideration include the following: How is analytical data for a new food, whether genetically engineered or produced by conventional methods, interpreted?
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1998. Trace elements in formulas based on cow and soy milk and in Austrian cow milk determined by inductively coupled plasma mass spectrometry.
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From page 101... ...
2003. Exploitation of molecular profiling techniques for GM food safety assessment.
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From page 102... ...
J Agric Food Chem 35:752758. Wang T, Wu J, Hartman R, Jia X, Egan RS.
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