New genetic tests for active ingredients should not replace trials in real people

Some of the biggest cosmetic companies have recently highlighted their use of DNA microarrays to identify the genes involved in skin health, and the possible compounds that could affect them.

In essence, the microarray is a small chip containing thousands of spots of different DNA sequences, called probes. These probes are designed and constructed by the researchers to match the genes of interest.

Small bits of messenger RNA (transcripts of the DNA that are used by the cell to make the proteins coded for in the DNA sequence) are taken from the biological sample and stained with fluorescent dye. These will bind to the matching probe on the chip and can be identified by their coloured glow.

In this way the microarrays can be used to test changes in gene expression – the more of a certain genetic sequence in the sample, the brighter the fluorescent glow.

P&G, for example, recently used this technique to investigate the differences in gene expression between old and young skin.

Having identified the genes whose activity differed between young and old skin, the company could then investigate possible active ingredients that might ‘repair’ these changes.

Such a tool is incredibly powerful in identifying genes involved in certain metabolic pathways and investigating the compounds that might effect their expression.

However, as with any new technology, it is important to remember what it does not do.

Proving that an active ingredient upregulates the expression of a gene whose activity normally decreases with age, does not prove that said ingredient will have an anti-ageing affect.

Metabolic pathways are incredibly complex, including a plethora of messenger molecules and proteins controlled by other genes that are not affected by the active ingredient in question. Changing one gene may have an affect on the end result; equally it may not.

In addition, even if the whole pathway is affected, and in the right direction, will this translate into an anti-ageing effect discernable by the naked eye? After all, your friends will not be complementing you on your gene expression levels, rather the improvement, or not, in your wrinkles.

Far from showing a product is the ‘real deal’, as claimed in the press release for one anti-ageing range, such investigations show only that gene expression levels are affected, not a decrease in wrinkles.

Furthermore, the models do not equate to a population of consumers. Different compounds may have different effects in different people, which will not be reflected by an in vitro ​model.

In short, DNA microarrays are an important tool in product development. In addition, they can go some way to investigating a product’s efficacy, but they are by no means the only tool and should be used only as a pre-screen before a product is tested in a population of real people.

Katie Bird is a science reporter writing on industry-related issues in several Decision News Media publications. If you would like to comment on this article, please e-mail Katie.Bird 'at' decisionnews.com.