AICAR

AICAR, also called acadesine in the literature, is the odd one out in a peptide catalog: it is a nucleotide analog. After uptake into the cell it is phosphorylated to ZMP, a molecule the cell perceives much like AMP. That is exactly what makes it useful as a tool. The energy sensor AMPK normally fires only when ATP is scarce and AMP abundant; ZMP delivers that signal without the actual ATP, ADP or AMP levels changing at all.

What an activated AMPK sets in motion in cells and tissues:

• more fatty acid oxidation
• more glucose uptake
• less anabolic synthesis, up to a near-complete halt of fatty acid and sterol synthesis in liver cells
• a push toward building new mitochondria

In the perfused rat hindlimb this was quantified in 1997: AMPK active in skeletal muscle, malonyl-CoA lowered, fatty acid oxidation raised 2.8-fold, glucose uptake increased. These adaptations resemble those of physical exertion, which is why AICAR was discussed early on under the catchphrase "exercise in a pill".

The molecule's history reaches back into the 1980s, and the documentation is correspondingly dense: AICAR has served for decades as a workhorse in studies of diabetes, the metabolic syndrome, exercise mimetics and the biology of mitochondria. The mechanism is resolved down to the level of phosphorylation, which makes the compound particularly handy for mechanistic questions.

A long research history and a clearly described mechanism do not change the fact that AICAR reaches deep into the cell's energy regulation.

• Several metabolic pathways at once: Direct AMPK activation shifts glucose and fatty acid utilization in parallel; preclinical studies document such changes clearly.
• Circulation and fatigue: Isolated reports mention circulatory effects and a passing exhaustion shortly after dosing.
• Injection site: Redness or a feeling of pressure are among the more common local observations.
• Four decades, still no long-term data: Robust human studies on prolonged use outside clinical protocols do not exist; the safety picture comes from animal and cell studies.

This summary is no substitute for medical advice.

• AICA riboside increases AMP-activated protein kinase, fatty acid oxidation, and glucose uptake in rat muscle - provides the readings from the rat hindlimb: AMPK active, malonyl-CoA lowered, fatty acid oxidation up 2.8-fold.
• AMPK: a nutrient and energy sensor that maintains energy homeostasis - review of AMPK, which switches on catabolic routes and throttles biosynthesis when energy runs low.
• Exercise mimetics targeting AMPK - places AICAR in the debate about exercise mimetics.