2-[2-(4-(trifluoromethyl)phenylamino)thiazol-4-yl]acetic acid (Activator-3) is a potent activator of AMPK

Adenosine monophosphate activated protein kinase contributes to skeletal muscle health through the control of mitochondrial function

Skeletal muscle is one of the largest organs in the body and the largest protein repository. Mitochondria are the main energy-producing organelles in cells and play an important role in skeletal muscle health and function. They participate in several biological processes related to skeletal muscle metabolism, growth, and regeneration. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor and regulator of systemic energy balance. AMPK is involved in the control of energy metabolism by regulating many downstream targets. In this review, we propose that AMPK directly controls several facets of mitochondrial function, which in turn controls skeletal muscle metabolism and health. This review is divided into four parts. First, we summarize the properties of AMPK signal transduction and its upstream activators. Second, we discuss the role of mitochondria in myogenesis, muscle atrophy, regeneration post-injury of skeletal muscle cells. Third, we elaborate the effects of AMPK on mitochondrial biogenesis, fusion, fission and mitochondrial autophagy, and discuss how AMPK regulates the metabolism of skeletal muscle by regulating mitochondrial function. Finally, we discuss the effects of AMPK activators on muscle disease status. This review thus represents a foundation for understanding this biological process of mitochondrial dynamics regulated by AMPK in the metabolism of skeletal muscle. A better understanding of the role of AMPK on mitochondrial dynamic is essential to improve mitochondrial function, and hence promote skeletal muscle health and function.

AMPK and Diseases: State of the Art Regulation by AMPK-Targeting Molecules

5′-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is an enzyme that regulates cellular energy homeostasis, glucose, fatty acid uptake, and oxidation at low cellular ATP levels. AMPK plays an important role in several molecular mechanisms and physiological conditions. It has been shown that AMPK can be dysregulated in different chronic diseases, such as inflammation, diabetes, obesity, and cancer. Due to its fundamental role in physiological and pathological cellular processes, AMPK is considered one of the most important targets for treating different diseases. Over decades, different AMPK targeting compounds have been discovered, starting from those that activate AMPK indirectly by altering intracellular AMP:ATP ratio to compounds that activate AMPK directly by binding to its activation sites. However, indirect altering of intracellular AMP:ATP ratio influences different cellular processes and induces side effects. Direct AMPK activators showed more promising results in eliminating side effects as well as the possibility to engineer drugs for specific AMPK isoforms activation. In this review, we discuss AMPK targeting drugs, especially concentrating on those compounds that activate AMPK by mimicking AMP. These compounds are poorly described in the literature and still, a lot of questions remain unanswered about the exact mechanism of AMP regulation. Future investigation of the mechanism of AMP binding will make it possible to develop new compounds that, in combination with others, can activate AMPK in a synergistic manner.

The effects of naringenin and naringin on the glucose uptake and AMPK phosphorylation in high glucose treated HepG2 cells

Background

Naringin and its aglycone naringenin are citrus-derived flavonoids with several pharmacological effects. On the other hand, the mechanism for the anti-diabetic effects of naringenin and naringin are controversial and remain to be clarified further.

Objective

This study examined the relationship between glucose uptake and AMP-activated protein kinase (AMPK) phosphorylation by naringenin and naringin in high glucose-treated HepG2 cells.

Methods

Glucose uptake was measured using the 2-NBDG fluorescent D-glucose analog. The phosphorylation levels of AMPK and GSK3β (Glycogen synthase kinase 3 beta) were observed by Western blotting. Molecular docking analysis was performed to evaluate the binding affinity of naringenin and naringin to the γ-subunit of AMPK.

Results

The treatment with naringenin and naringin stimulated glucose uptake regardless of insulin stimulation in high glucose-treated HepG2 cells. Both flavonoids increased glucose uptake by promoting the phosphorylation of AMPK at Thr172 and increased the phosphorylation of GSK3β. Molecular docking analysis showed that both naringenin and naringin bind to the γ-subunit of AMPK with high binding affinities. In particular, naringin showed higher binding affinity than the true modulator, AMP with all three CBS domains (CBS1, 3, and 4) in the γ-subunit of AMPK. Therefore, both naringenin and naringin could be positive modulators of AMPK activation, which enhance glucose uptake regardless of insulin stimulation in high glucose-treated HepG2 cells.

Conclusions

The increased phosphorylation of AMPK at Thr172 by naringenin and naringin might enhance glucose uptake regardless of insulin stimulation in high glucose treated HepG2 cells.

Evaluation of Biosafety, Antiobesity, and Endothelial Cells Proliferation Potential of Basil Seed Extract Loaded Organic Solid Lipid Nanoparticle

The present study aimed to synthesize solid lipid nanoparticles to enhance liposome-assisted intracellular uptake of basil seed active components in adipocytes and vascular smooth muscle cells to attain increased bioavailability. To obtain solid lipid nanoparticle (SLNp), the water phase containing basil seed extract (BSE) was encapsulated with lipid matrix containing chia seed phospholipids using homogenization and cold ultra-sonication method. The physicochemical characterization of BSE loaded solid lipid nanoparticles (BSE-SLNp) has been analyzed using Zetasizer, FT-IR, and TEM. The BSE-SLNp showed an average diameter of 20-110 nm on the day of preparation and it remains the same after 60 days of storage. The cytotoxicity assay confirmed that the BSE-SLNp did not produce toxicity in hMSCs, preadipocytes, or human umbilical vein endothelial cells (HUVECs) until the tested higher dose up to 64 μg/ml. During effective dose determination, 4 μg/ml of BSE-SLNp confirmed non-toxic and enhanced metabolic function in hMSCs, preadipocytes, and HUVECs. Biosafety assay confirmed normal nuclear morphology in PI staining and high mitochondrial membrane potential in JC-1 assay within 48 h in hMSCs. The maturing adipocyte treated with 4 μg/ml of BSE-SLNp significantly increased the mitochondrial efficiency and fatty acid beta-oxidation (PPARγC1α, UCP-1, and PRDM-16) related gene expression levels. Oxidative stress induced HUVECs treated with 4 μg/ml of BSE-SLNp potentially enhanced antioxidant capacity, cell growth, and microtubule development within 48 h H₂O₂ induced oxidative stressed HUVECs have shown 39.8% viable cells, but treatment with BSE-SLNp has shown 99% of viable cells within 48 h confirmed by Annexin-V assay. In addition, mitochondrial membrane potential (Δψ_m) increased to 89.4% confirmed by JC-1 assay. The observed DNA integrity, cell viability was confirmed by increased antioxidant and tumor suppressor-related gene expression levels. VEGF expression has been significantly increased and pro-inflammation-related mRNA levels were decreased in BSE-SLNp treated cells. In conclusion, enhanced adipocyte fatty acid oxidation is directly associated with decreased adipocytokine secretion which arrests obesity-associated comorbidities. In addition, suppressing vascular cell oxidative stress and metabolic inflammation supports vascular cell proliferation and arrests ageing-related vascular diseases.

Design, synthesis, and biological evaluation of 1,2,4-oxadiazole-containing pyrazolo[3,4-b]pyridinones as a new series of AMPKɑ1β1γ1 activators

Adenosine monophosphate-activated protein kinase (AMPK) plays a key role in maintaining whole-body homeostasis and has been regarded as a therapeutic target for the treatment of diabetic nephropathy (DN). Herein, a series of 1,2,4-oxadiazole-containing pyrazolo[3,4-b]pyridinone derivatives is reported as AMPKɑ1β1γ1 activators. The in vitro biological assay demonstrated that compounds 12k (EC₅₀ [AMPKα1γ1β1] = 180 nM) and 13q (EC₅₀ [AMPKα1γ1β1] = 2 nM) displayed significant enzyme activation. Mechanism studies indicated that both compounds reduced the levels of reactive oxygen species in a rat kidney fibroblast cell line (NRK-49F) stimulated by transforming growth factor-β and induced early apoptosis of NRK-49F cells at 10 μM. Molecular docking studies suggested that 13q exhibited critical hydrogen-bond interactions with the critical amino acid residues Lys29, Lys31, Asn111, and Asp88 at the binding site of the AMPK protein. These results enrich the structure pool of AMPK activators and provide novel lead compounds for the subsequent development of compounds with a promising therapeutic potential against DN.

Small-Molecule Kinase Inhibitors for the Treatment of Nononcologic Diseases

Great successes have been achieved in developing small-molecule kinase inhibitors as anticancer therapeutic agents. However, kinase deregulation plays essential roles not only in cancer but also in almost all major disease areas. Accumulating evidence has revealed that kinases are promising drug targets for different diseases, including cancer, autoimmune diseases, inflammatory diseases, cardiovascular diseases, central nervous system disorders, viral infections, and malaria. Indeed, the first small-molecule kinase inhibitor for treatment of a nononcologic disease was approved in 2011 by the U.S. FDA. To date, 10 such inhibitors have been approved, and more are in clinical trials for applications other than cancer. This Perspective discusses a number of kinases and their small-molecule inhibitors for the treatment of diseases in nononcologic therapeutic fields. The opportunities and challenges in developing such inhibitors are also highlighted.

AMP-activated protein kinase: the current landscape for drug development

Since the discovery of AMP-activated protein kinase (AMPK) as a central regulator of energy homeostasis, many exciting insights into its structure, regulation and physiological roles have been revealed. While exercise, caloric restriction, metformin and many natural products increase AMPK activity and exert a multitude of health benefits, developing direct activators of AMPK to elicit beneficial effects has been challenging. However, in recent years, direct AMPK activators have been identified and tested in preclinical models, and a small number have entered clinical trials. Despite these advances, which disease(s) represent the best indications for therapeutic AMPK activation and the long-term safety of such approaches remain to be established.