IGF-1 analogue mecasermin boosts athletes' endurance capacity
Medical doses of the IGF-1 variant mecasermin rinfabate have no effect on athletes' muscle and fat mass, but do result in increased endurance capacity. Endocrinologists at the University of Southampton in England discovered this when they gave recreational athletes this IGF-1 complex for 28 days. The researchers think it's time for the WADA to develop a doping test for mecasermin rinfabate.
IGF-1 and IGFBP-3
IGF-1 has become as normal as growth hormone and testosterone in elite circles of chemical athletes. These athletes usually use slightly tweaked versions of IGF-1. These are less quickly neutralised by enzymes and transport proteins than ordinary IGF-1, which disappears in a flash out of the bloodstream after it has been injected.
The inventors of the preparation that the researchers used found another solution for this problem: they attached the IGF-1 molecule to the transport protein IGFBP-3. IGFBP-3 protects IGF-1 against attacks from enzymes and releases the hormone gradually. As a result, users only have to inject it once a day, and, unlike IGF-1, the IGF1-IGFBP-3 complex has no dramatic effects on glucose levels.
Iplex and Increlex
The researchers used Iplex, manufactured by Insmed. At the start of this century Insmed funded studies on IGF-1-IGFBP-3, but decided to halt production in 2009. [biospace.com 7/27/2009.] The researchers seem to have used preparations that Insmed had stored in the deep freeze.
Mecasermin rinafabate is still on the market, under the name of Increlex, manufactured by Ipsen Biopharmaceuticals.
The researchers gave 56 recreational athletes, all of whom did intensive training at least twice a week, daily injections containing 30 or 60 mg IGF-1-IGFBP-3 for 28 days. During this period the subjects' bodyweight, lean body mass and fat mass did not change.
The researchers also added the proviso that they had used medical doses and that they didn't know what effects such high doses might have, or what the effect of combining IGF-1-IGFBP-3 with growth hormone might be.
The subjects' maximal oxygen uptake [VO2max], the most important measure of endurance capacity, did increase as a result of the administration of the IGF-1-IGFBP-3 complex. In the figure below the researchers make a distinction between the male and female subjects. The 30 mg dose was not as effective as the 60 mg dose.
"There are no confirmed cases of elite athletes obtaining and misusing rhIGF-I/rhIGFBP-3, but it would seem an attractive anabolic agent with lower risk of side effects, compared with either IGF-I alone or insulin", the researchers wrote.
"This study demonstrates that 28 days of IGF-I/IGFBP-3 administration improves aerobic fitness but has no effect on body fat or lean body mass in recreational athletes. The significance of this improvement in elite athletes requires further investigation, as do the mechanisms underlying the benefits on aerobic performance."
"The results of this study support the inclusion of IGF-I on the WADA list of prohibited substances and highlight the need to develop methods for detecting IGF-I misuse."
J Clin Endocrinol Metab. 2015 Aug;100(8):3126-31.
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