
Jannik Sinner’s stellar season has been somewhat overshadowed by a shock doping case. On August 20th, just before the US Open, news broke of Sinner’s two failed drug tests from March of this year - causing significant backlash from analysts, pundits and fellow players. The Tennis Anti-Doping Programme cleared the World No.1 of any wrongdoing - a decision that the World Anti-Doping Agency has recently appealed. While performance enhancement is not the only factor the WADA will look at, it should hold significant weight in the WADA’s decision, so let’s take a look at the chemistry behind clostebol and to what extent it could improve performance.
Clostebol is a weak anabolic-androgenic steroid - specifically, a chlorinated derivative of testosterone. Many anabolic-androgenic steroids appear on the WADA’s list of banned substances due to their structural similarity to testosterone, allowing the drug to mimic actions of testosterone in the body. Closetbol can enhance performance via a few different mechanisms; binding to androgen receptors triggers a series of cellular processes that activate genes responsible for protein synthesis; inhibition of catabolic processes reduces the breakdown of muscle proteins, maintaining muscle mass during periods of physical stress; and shifting the body towards an anabolic state can improve protein synthesis. Closetbol acetate also impacts the production and release of erythropoietin, a hormone responsible for red blood cell production - increased red blood cell counts can improve oxygen delivery to tissue and enhance endurance. Compared to other steroids, closetbol has relatively low androgenic activity, reducing effects related to the development of male characteristics typically associated with testosterone.
In the body, clostebol is primarily metabolised in the liver. Common enzyme modifications involve redox at various positions on the steroid backbone, and conjugation with glucuronic acid which increases the solubility of metabolites in water - supporting excretion via urine. Closetbol and its primary metabolites are detected using techniques such as gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry, which are able to detect at concentrations down to nanogram-per-milliter levels (a billionth of a gram - the exact amount that was detected in Sinner’s case). Typically doping laboratories wil look for clostebol metabolites rather than the drug itself, due to glucuronide-conjugated forms especially being more readily detected.
So where is the line between intentional ingestion and contamination? Within the tennis community, controversy exists over whether a billionth of a gram is truly insignificant - after all, doping tests are designed to detect at these levels for good reason. In the case of clostebol, levels below 2-5ng/mL are consistent with incidental exposure depending on the sensitivity of the test, with concentrations above 10ng/mL being typical with intentional use, which is substantially more than what was detected in Sinner’s case. This gives a lot of credibility to Sinner’s defence, as the quantity detected is well within the contamination range.
Consumption can be estimated depending on the measured metabolite concentration and data on the conversion of the parent compound into the metabolite, but this will vary depending on individual metabolisms, formulation and time since consumption. Considering typical dosages for performance enhancement and a common conversion rate of 50-70% within 24 hours, it is highly unlikely Sinner gained much of a performance advantage from the quantity detected. Although the WADA is likely to consider other factors in their decision, Sinner should feel relatively confident in his case.
Research:
Closetbol is a type of anabolic-androgenic steroid
Closetbol is the 4-chloro derivative of testosterone
Chlorination prevents conversion to dihydrotestosterone while rendering the chemical incapable of conversion to estrogen
Structurally similar to testosterone and produce effects by binding to the androgen receptor → enhanced anabolic properties and minimised androgenic effects
Used to increase muscle size, strength, performance
Closetbol is a weak AAS and is currently banned by the WADA
Closetbol acetate ointment has opthamlmological and dermatological use, and in countries such as Italy is available without a prescription and is used as a topical cream or spray for skin wounds
Trofodermin, which was the source of contamination in Sinner’s case, does contain large doping warnings (as closetbol appears on the WADA’s list of banned substances)
How does closetbol enhance performance: (as clostebol acetate)
Mimics actions of testosterone - binding to androgen receptors in target tissues such as muscles, bones and the central nervous system
When closetbol acetate attaches to these receptors, it triggers a cascade of cellular processes that lead to the activation of specific genes responsible for protein synthesis
Closetbol binds to androgen receptors - proteins that respond to androgens such as testosterone and initiate the expression of genes that control muscle growth
Closetbol also inhibits catabolism and reduces the breakdown of muscle proteins, ensuring muscle mass is maintained and improved during periods of physical stress
One primary mechanism is through increasing nitrogen retention which enahnces protein synthesis capacity
Body stays in a more anabolic state
Closetbol acetate also impacts the production and release of erythropoietin, a hormone responsible for red blood cell production
Higher red blood cell counts improve oxygen delivery to tissue which enhances endurance
Closetbol has relatively low androgenic activity compared to other steroids
The addition of the chloro group at the fourth carbon of the steroid
So fewer effects from high androgen levels (effects associated with testosterone)
Closetbol interactions in the body:
Closetbol acetate is also metabolised in the liver, where it undergoes enzymatic transformations to increase water solubility and ease of excretion
Liver metabolism involves the reduction of the 17-keto group and conjugation with glucuronic acid or sulfate
Reduction of ketone group at C3 position of steroid backbone
Oxidation at other positions, creating hydroxylated derivatives
Conjugation reactions (combined with glucoronic acid or sulfate, improving water solubility for excretion)
For a single dose of clotebol, the drug can be detected in the urine for several days to weeks
Glucuronide-conjugated forms of closetbol metabolites are typically tested for, as they are excreted in higher amounts
Anti-doping laboratories typically aim to detect the presence of metabolites at levels that indicate deliberate use rather than contamination from environmental sources
The mere detection of closetbol, regardless of amount, is considered a doping violation by the WADA as it is classified as a prohibited substance
Concentrations in the range of nanograms per milliliter in urine samples are rypically associated with active or recent use of the steroid
A lot of emphasis on ‘billionth of a gram’ online; but the dosage at which most drugs are ingested indicate that this is not necessarily a negligible amount
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