AICAR

Overview

AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) is a naturally occurring intermediate in de novo purine biosynthesis. Its cell-permeable form, AICA riboside (acadesine), has become one of the most widely used pharmacologic tools for studying AMP-activated protein kinase (AMPK) signaling in skeletal muscle, liver, adipose tissue, and the nervous system.

AICAR gained broad research attention following a landmark 2008 study by Narkar and colleagues showing that chronic AICAR administration in sedentary mice induced gene expression patterns and endurance improvements similar to those produced by exercise training. This "exercise in a pill" finding spurred significant interest from metabolism researchers, as well as attention from anti-doping authorities — AICAR is included on the World Anti-Doping Agency prohibited list.

AICAR is strictly a research chemical and is not a peptide. It is sometimes catalogued alongside peptide research compounds because of its overlap with metabolic peptides such as FGF21 and irisin, and with AMPK-activating agents like metformin.

Structure / Chemistry

• Chemical class: purine nucleotide analog (imidazole carboxamide)
• Molecular formula (free riboside): C9H14N4O5
• Molecular weight (riboside, acadesine): 258.23 g/mol
• Phosphorylated intracellular form: ZMP (AICA ribotide)

Acadesine is the nucleoside precursor; once taken up by cells via adenosine transporters, it is phosphorylated by adenosine kinase to ZMP, the active intracellular species. ZMP mimics AMP by binding the gamma subunit of AMPK, producing allosteric activation without altering cellular ATP/AMP ratios.

Mechanism of Action

AICAR acts as an AMP mimetic through its intracellular metabolite ZMP:

• Allosteric AMPK activation via binding to the gamma regulatory subunit
• Promotion of Thr172 phosphorylation on the AMPK alpha subunit by upstream kinases LKB1 and CaMKK2
• Downstream metabolic shifts, including increased fatty acid oxidation, glucose uptake through GLUT4 translocation, mitochondrial biogenesis via PGC-1alpha, and inhibition of anabolic pathways (ACC, HMG-CoA reductase, mTORC1)

AMPK activation by AICAR produces effects that partially overlap with exercise training: increased oxidative enzyme expression, improved insulin sensitivity, and enhanced mitochondrial content in skeletal muscle. These effects are context-dependent and vary across tissues.

Research Summary

Acadesine has also been investigated in cardiac ischemia-reperfusion, chronic lymphocytic leukemia, and inflammatory disorders, though none of these programs have reached broad clinical approval.

Pharmacokinetics

AICA riboside is administered intravenously or subcutaneously in research protocols due to limited oral bioavailability. Plasma half-life is short — approximately 1–2 hours in rodents and under an hour in humans — reflecting rapid cellular uptake and renal clearance.

Intracellular phosphorylation to ZMP is rate-limiting and depends on tissue-specific adenosine kinase activity. Tissues with high adenosine kinase (liver, skeletal muscle) accumulate ZMP most efficiently. Unmetabolized AICAR and its degradation products are excreted in urine.

Common Discussion Topics

• Status on the WADA prohibited list and detectability in athlete urine samples
• Comparison with other AMPK activators (metformin, salicylate, compound 991)
• Differences between AICAR's acute and chronic effects on muscle phenotype
• Limitations of ZMP as an AMP mimetic, including off-target effects on adenosine-binding enzymes
• Tissue-selective AMPK activation strategies beyond AICAR

Related Compounds

• FGF21 — metabolic peptide with partially overlapping effects
• Irisin — exercise-induced myokine with metabolic reprogramming activity
• Adiponectin — AMPK-activating adipokine
• 5-Amino-1MQ — NNMT inhibitor studied in related metabolic context
• Humanin — mitochondrial peptide modulating metabolic stress

Educational information only. AICAR is a research chemical, is prohibited in competition by WADA, and is not intended for human performance use. This article does not constitute medical or performance advice.