AMPK activators: mechanisms of action and physiological activities Experimental & Molecular Medicine

It turns out that AICAR mimics the effects of exercise very precisely and that repeated administration of AICAR has effects similar to long-term exercise. The first study of the safety and tolerance of AICAr was done in 1991, much before the recognition of AICAr as an AMPK agonist to establish pharmacokinetics of a drug that raised interest as a novel adenosine-regulating agent 49. Adenosine is a potent vasodilator that plays a key role in reducing ischemia/reperfusion injury, but the applications for systemic adenosine are limited owing to peripheral hemodynamic actions 13. As shown in Figure 1, AICAr shares structural similarities with adenosine, and therefore, can increase the extracellular concentrations of adenosine by competing for the nucleoside transporter 20. In addition, AICAR increases intracellular concentrations by inhibiting adenosine deaminase and increasing the production of adenosine rather than inosine from ATP catabolism. Several animal studies performed in the 1980s demonstrated that AICAr or acadesine infusion improved postischemic recovery in the heart 53,54, and prompted the first international randomized studies in human participants undergoing coronary artery bypass graft surgery (CAGS).

• Because of the favorable physiological outcomes of AMPK activation on metabolism, AMPK has been considered to be an important therapeutic target for controlling human diseases including metabolic syndrome and cancer.
• Studies have demonstrated that AICAR can mimic the effects of exercise by enhancing muscle endurance and performance.
• In contrast, myeloid deletion of SIRT1 increases macrophage inflammation through promotion of pro-inflammatory M1 polarization coupled with inhibition of M2 activation.

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These results indicate that pharmacologic activation of the PPARδ genetic program in adult C57Bl/6J mice is insufficient to promote a measurable enhancement of treadmill https://colompack.co/2025/01/29/understanding-steroids-uses-risks-and-guidelines-2/ endurance. AMPK and SIRT1 share striking similarities in nutrient sensing and regulation of energy metabolism. Recent studies have disclosed a crosstalk between these two in regulation of metabolic pathways. For instance, AMPK can be an upstream signal to increase SIRT1 activity via inducing fatty acid oxidation and increasing the agonist NAD+ levels, leading to the deacetylation and activation of PGC-1α in muscle 35.

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In the brain, seven days of AICAR or running increased dentate gyrus BDNF protein levels and cell proliferation. However, longer pharmacological activation did not result in changes in cell genesis or neurotrophin levels and may even be detrimental. In particular, microarray analysis showed an inversion of DG gene regulation, such as increased expression of pro-apoptotic genes, with long-term AICAR treatment. In addition, markers of inflammation were up-regulated in the DG and LEC after fourteen days of AICAR treatment, whereas running reduced inflammatory cytokine levels. Thus, while both interventions may have similar effects on muscle energy metabolism, only running continuously benefits brain function. The 5′-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is activated by increases in cellular ATP/AMP ratio and plays an important role in regulating glycolytic activity and maintaining energy balance at both cellular and whole body levels 10.

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Consequently, once endurance athletes got word of this amazing compound, AICAR was being used without any regulation or fear of testing until 2011. Physiological AMPK activation involves phosphorylation of Thr-172 within the activation loop of the KD in the AMPKα catalytic subunit. Two upstream kinases, LKB118 and CaMKKβ (Ca2+/calmodulin-dependent protein kinase β),19 have been extensively documented to phosphorylate Thr-172 of the AMPKα subunit. Treatments that deplete cellular ATP do not effectively activate AMPK in LKB1-negative tumors because the basal activity of CaMKKβ is too low to affect the phosphorylation status of AMPKα Thr172, although the increase in AMP due to ATP depletion makes the AMPK α-subunit a better substrate for CaMKKβ. However, these treatments can cause AMPK activation under conditions that elevate intracellular Ca2+.

Blood glucose was measured with an OneTouch Ultural Glucose meter (Lifescan, Mulpitas, CA). Serum insulin levels were measured using rat insulin enzyme-linked immunosorbent assay (ELISA) kits (Crystal Chem, Downers Grove, IL). Glucose tolerance test (GTT) and Insulin tolerance test (ITT) were performed as we previously described 38. For GTT, mice were fasted overnight, and blood glucose was measured immediately before and 15, 30, 60, 90, and 120 min after an intraperitoneal (i.p.) injection of glucose (1.2–1.8 g/kg of body weight). For ITT, mice were injected intraperitoneally with 1–1.8 unit/kg of human insulin (Humulin R, Eli Lilly, Indiana, IN) after a 6-hr food removal, and glucose levels were measured at different time points (0, 15, 30, 60, 120 minutes). Bold, underlined Z-ratio values represent classes with a Selector value above 2 or below −2.

High throughput DNA-binding assays may also identify the whole spectrum of transcription factor – DNA interactions sensitive to AICAR. To explain the broad effect of AICAR on transcriptional activation we considered the interaction with general component of the transcription machinery. However, this is unlikely to be the case, since STAT6-dependent and HIF-evoked gene expression remained unaltered in AICAR-treated cells.

However, we observe that the beneficial effects of AICAR and exercise on the brain (increased DG cell genesis and BDNF levels at 7 days) precede brain energy metabolism protein level changes (at 14 days in DG and LEC), indicating these may be unnecessary for enhancement of neural plasticity. Indeed, in Alzheimer’s Disease mouse models, prolonged brain AMPK activation may contribute to detrimental effects on synaptic plasticity and memory formation, by inducing long-lasting cellular stress and impairing protein synthesis 73. Type I fibers preferentially express enzymes that oxidize fatty acids, contain slow isoforms of contractile proteins and are more resistant to fatigue than glycolytic fibers. Type II fibers preferentially metabolize glucose and express the fast isoforms of contractile proteins. Endurance exercise training triggers a remodeling program in skeletal muscle that progressively enhances performance in athletes such as marathon runners, mountain climbers and cyclists.