Selective Androgen Receptor Modulators (SARMs) provide the benefits of traditional anabolic/androgenic steroids such as testosterone (including increased muscle mass, fat loss, and bone density), while showing a lower tendency to produce unwanted side effects. They are a unique class of molecules currently under development for treatment of a variety of diseases that were previously treated with anabolic steroids and other medications. SARMs have been studied and developed since 1998, and as of this writing (2009) it should be stated that they are still very much in the infancy of their development and marketing.
Briefly and simply stated, the Androgen Receptor (AR) is the cellular receptor that androgens (like testosterone and other anabolic steroids) bind to. This bound androgen/receptor then combine with another similar combination (usually another androgen/androgen-receptor pair), and travel to the cell’s nucleus, where gene transcription is induced. This is one known mechanism of how androgens such as anabolic steroids exert their effects on cells. SARMs have the potential to take the place of the androgen, for all practical intents and purposes, and therefore exert many of the same positive effects on muscle tissue as anabolic steroids (such as testosterone).
The Androgen Receptor plays a critical role in the development and function of primary and accessory sexual organs, skeletal muscle, and bone, as well as several other organs. When Selective Androgen Receptor Modulators bind to the receptor, they demonstrate anabolic (hypertrophic) activity in both muscle and bone, making them ideal candidates for androgen replacement therapy, muscle wasting, and treating Osteoporosis. In theory, they bind to the receptor and place it in a conformation that is significantly different than typical androgen receptors stimulators (such as steroids), and therefore are able to alter the gene-transcription process in a manner that is tissue specific.
It is this specificity that makes these receptor modulators able to selectively cause muscle growth, while reducing or eliminating unwanted secondary effects.
ANDROGEN RECEPTOR ACTION:
The Androgen Receptor is maintained in an inactive complex by HSP 70 and HSP 90 and corepressors (CoR). Upon ligand binding, the receptor homodimerizes and enters the nucleus. The receptor is basally phosphorylated in the absence of hormone and hormone binding increases the phosphorylation status of the receptor (P). The AR binds to the ARE on the promoter of androgen responsive genes, leading to the recruitment of coactivators (p160s, CBP, TRAP, ARAs) and general transcription factors (GTF), leading to gene transcription.(Adapted from Open Access Journal of Nuclear Access Signaling)
Ergo, unlike anabolic steroids, SARMs generally produce fewer unwanted side effects on non-target tissues such as the prostate, hairline, sebaceous glands, and secondary sexual organs. Some SARMs have even been developed specifically for the treatment of those kinds of side effects (i.e. for benign prostate hypertrophy).
Current oral androgen replacement therapy is very limited, with the only available forms of testosterone being Andriol (which is widely seen as expensive and ineffective) and Methyltestosterone (which is liver toxic). SARMs represent an alternative to the currently available oral testosterone preparations, and offer the user molecules that exhibit high oral bioavailability without the liver toxicity.
Although these molecules are tissue-selective with regards to their effects, they are not perfectly tissue-selective. Some display a disparity of anabolic (*tissue building) versus androgenic (*secondary sexual characteristic promoting) effect as high as 10:1 (although it should be noted that some have a much lower ratio). In practical terms, it would be highly unlikely that an effective muscle building dose would cause any noticeable side effects, and especially not when compared to traditionally prescribed anabolic steroids such as testosterone.
At this stage of development there are no SARMs available on the legitimate pharmaceutical market, although one (Ostarine) has made it into the third and last phase of clinical development (and is available on the black market, in liquid “research” form, from one supplier within the United States. Unfortunately, at this early stage of development, the exact mechanisms of their tissue selective activity is not entirely understood, nor is the full scope of their pharmacokinetic and pharmacodynamic activity.
There are numerous SARMs currently in the developmental stage with varying degrees of anabolic and androgenic activity, and varying potential for side effects. In general, though, the majority of them produce few side effects and have anabolic ratings similar to testosterone.
They typically display high oral bioavailability, and therefore most SARMs under development are going to eventually enter the market as oral medications. .
Although they have been banned for the past few years by the World Anti-Doping Agency, and there have been efforts underway to develop a testing protocol for them, there is currently no accepted testing procedure in place. The relatively short half life of SARMs, the uniqueness of their structure, their effectiveness, and the fact that research into their development is still in its infancy, presents a new and novel problem for doping authorities everywhere.