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DNA: Hard Evidence of Cosmeceutical Claims
By: Katie Schaefer, Cosmetics & Toiletries magazine
Posted: May 4, 2009, from the May 2009 issue of Cosmetics & Toiletries.
Products have evolved to serve multiple functions, treading the line between industries and stirring the emergence of such terms as cosmeceutical and nutricosmetic. While some dismiss this as mere marketing, the associated claims cannot be ignored; and as an overabundance of claims becomes more indecipherable for the consumer, regulatory bodies such as the Better Business Bureau and the US Food and Drug Administration are cracking down on manufacturers for the messages they convey, requiring they be backed by solid science.
To support finished product or raw material claims, Anna Langerveld, PhD, of Genemarkers LLC, has developed two in vitro methods—the Affymetrix microarray and the Taqman Real Time Polymerase Chain Reaction (PCR)—to measure the up-regulation or down-regulation of genes.
Before tests are performed, RNA solutions are prepared and converted into complementary DNA (cDNA) using the reverse transcriptase enzyme. For the Affymetrix microarray, the cDNA samples are converted back into fluorescently labeled cRNA. This cRNA is fragmented into small pieces and loaded onto a gene chip. “The labeled cRNA binds to its complementary DNA sequence on the gene chip and the fluorescence is measured,” said Langerveld.
For the Real Time PCR method, cDNA is mixed with small pieces of DNA called primers and probes. These pieces contain DNA sequences and bind only to specific genes of interest. The enzyme taq polymerase is added to the reaction and the mixture is placed in a PCR device to create millions of copies of the specific cDNA, determined by the primer or probe. Fluorescence is used in both methods.
Scanning the Genome
In the Affymetrix mircroarray, samples with more cRNA for a given gene generate a larger fluorescent signal. “Fluorescent signals for each gene are compared across all the samples,” said Langerveld. This method differs only slightly from the PCR method, where the probe has a fluorescent tag and is measured by the device. Again, the greater amounts of cDNA for a specific gene will generate a larger fluorescent signal, which is compared across all samples.