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Peptides the centre of latest sports doping scandal; but what are they?

Recently, human growth hormone (or HGH) has found media attention for its use by sports people to gain an unfair competitive advantage.

HGH is naturally produced in the body just below the brain in the anterior pituitary gland as part of a family of peptide hormones. HGH performs a wide (and not yet fully understood) range of signaling functions in the body, such as stimulating the immune system and strengthening bone through increased calcium retention; but, from a doping point of view, it’s ability to trigger the secretion of insulin like growth factor (IGF-1) is of interest.

IGF-1 stimulates cartilage producing cells, promotes the formation of lean muscle mass and the generation of connective tissue. The hormone, when at elevated levels, is believed to aid in the healing process and is typically used to treat growth and ageing related diseases. However, when used in sport, it is believed to shorten the time for which an injured player is unavailable.

How peptides are made (some science content follows)

Peptide hormones are made from individual molecules known as amino acids, which join together head-to-tail to form long chains.

There are twenty-one different amino acids that are used by the body, each providing a unique property by having a different chemical group attached to the side of the molecule. Therefore, by stringing together a variety of these amino acids in a certain order, the body can create very specific molecules that have a unique structure and function. These strings are known as peptides; if they are made longer, then they form a protein.

A healthy person naturally produces HGH, and its levels constantly change, and are related to a number of factors, such as the amount of exercise performed, the time of day, and the type of diet. The release of HGH is, in turn stimulated and controlled by a second set of peptide hormones.

When sports and peptides join forces

Doping seeks to achieve an increase in HGH in two ways; by the direct injection of a man-made HGH molecule, or by the introduction of one of these secondary hormones.

Direct hormone injection is banned by all the sporting bodies, and elevated levels in the blood carries a significant risk of detection as the levels of HGH in the system are raised for a number of days.

The second, and more difficult to detect method, is to use fragments of these secondary hormones. Very short fragments of the peptides (sometimes as short as six amino acids – known as growth hormone releasing peptide or GHRP) have been identified as retaining the ability to influence HGH production.  Importantly, these short peptide sequences are easily synthesised, and difficult to detect.

The compounds, when injected, cause a huge increase in HGH production, which is short lived. This spike in HGH is also used to mask the use of ‘straight’ HGH, as it returns the levels back to normal much more quickly; because of this, it is relatively easy to successfully dope.

The problem arises when new peptide sequences are developed that are not yet tested and regulated, but provide a benefit to the athlete. One of these is the HGH fragment known as AOD-9604, which is used to treat obesity as it contains the amino acid sequence which enables the fat-burning mechanisms that are regulated by HGH

There is a constant arms race between those seeking to gain an advantage via the use of ‘supplements’, and the doping agencies determination of the ‘fairness’ of these advantages. The question arises of what ‘peptides’ the doping scandal recently refers to; are they innocent, not yet regulated, or a fully aware attempt to cheat?

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