AMPK (AMP-activated protein kinase) is activated allosterically by AMP and by phosphorylation of Thr172 within the catalytic alpha subunit. Here we show that mutations in the regulatory gamma subunit reduce allosteric activation of the kinase by AMP. In addition to its allosteric effect, AMP significantly reduces the dephosphorylation of Thr172 by PP (protein phosphatase)2Calpha. Moreover, a mutation in the gamma subunit almost completely abolishes the inhibitory effect of AMP on dephosphorylation. We were unable to detect any effect of AMP on Thr172 phosphorylation by either LKB1 or CaMKKbeta (Ca2+/calmodulin-dependent protein kinase kinase beta) using recombinant preparations of the proteins. However, using partially purified AMPK from rat liver, there was an apparent AMP-stimulation of Thr172 phosphorylation by LKB1, but this was blocked by the addition of NaF, a PP inhibitor. Western blotting of partially purified rat liver AMPK and LKB1 revealed the presence of PP2Calpha in the preparations. We suggest that previous studies reporting that AMP promotes phosphorylation of Thr172 were misinterpreted. A plausible explanation for this effect of AMP is inhibition of dephosphorylation by PP2Calpha, present in the preparations of the kinases used in the earlier studies. Taken together, our results demonstrate that AMP activates AMPK via two mechanisms: by direct allosteric activation and by protecting Thr172 from dephosphorylation. On the basis of our new findings, we propose a simple model for the regulation of AMPK in mammalian cells by LKB1 and CaMKKbeta. This model accounts for activation of AMPK by two distinct signals: a Ca2+-dependent pathway, mediated by CaMKKbeta and an AMP-dependent pathway, mediated by LKB1.

AMP-activated protein kinase (AMPK) is a major therapeutic target for the treatment of diabetes. We investigated the effect of a short-term overexpression of AMPK specifically in the liver by adenovirus-mediated transfer of a gene encoding a constitutively active form of AMPK␣2 (AMPK␣2-CA). Hepatic AMPK␣2-CA expression significantly decreased blood glucose levels and gluconeogenic gene expression. Hepatic expression of AMPK␣2-CA in streptozotocin-induced and ob/ob diabetic mice abolished hyperglycemia and decreased gluconeogenic gene expression. In normal mouse liver, AMPK␣2-CA considerably decreased the refeeding-induced transcriptional activation of genes encoding proteins involved in glycolysis and lipogenesis and their upstream regulators, SREBP-1 (sterol regulatory element-binding protein-1) and ChREBP (carbohydrate response element-binding protein). This resulted in decreases in hepatic glycogen synthesis and circulating lipid levels. Surprisingly, despite the inhibition of hepatic lipogenesis, expression of AMPK␣2-CA led to fatty liver due to the accumulation of lipids released from adipose tissue. The relative scarcity of glucose due to AMPK␣2-CA expression led to an increase in hepatic fatty acid oxidation and ketone bodies production as an alternative source of energy for peripheral tissues. Thus, short-term AMPK activation in the liver reduces blood glucose levels and results in a switch from glucose to fatty acid utilization to supply energy needs.

The alkaloid drug berberine (BBR) was recently described to decrease plasma cholesterol and triglycerides (TGs) in hypercholesterolemic patients by increasing expression of the hepatic low density lipoprotein receptor (LDLR). Using HepG2 human hepatoma cells, we found that BBR inhibits cholesterol and TG synthesis in a similar manner to the AMP-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide 1-b-ribofuranoside (AICAR). Significant increases in AMPK phosphorylation and AMPK activity were observed when the cells were incubated with BBR. Activation of AMPK was also demonstrated by measuring the phosphorylation of acetyl-CoA carboxylase, a substrate of AMPK, correlated with a subsequent increase in fatty acid oxidation. All of these effects were abolished by the mitogen-activated protein kinase kinase inhibitor PD98059. Treatment of hyperlipidemic hamsters with BBR decreased plasma LDL cholesterol and strongly reduced fat storage in the liver. These findings indicate that BBR, in addition to upregulating the LDLR, inhibits lipid synthesis in human hepatocytes through the activation of AMPK. These effects could account for the strong reduction of plasma TGs observed with this drug in clinical trials.-Brusq, J-M., N. Ancellin, P. Grondin, R. Guillard, S. Martin, Y. Saintillan, and M. Issandou. Inhibition of lipid synthesis through activation of AMP kinase: an additional mechanism for the hypolipidemic effects of berberine.

Modification of the hydantoin ring in the previously described lead compound 2a has led to the discovery of compound 12a, tadalafil, a highly potent and highly selective PDE5 inhibitor. The replacement of the hydantoin in compound 2a by a piperazinedione ring led to compound cis-11a which showed similar PDE5 inhibitory potency. Introduction of a 3,4-methylenedioxy substitution on the phenyl ring in position 6 led to a potent PDE5 inhibitor cis-11c with increased cellular potency. Optimization of the chain on the piperazinedione ring led to the identification of the racemic cis-N-methyl derivative 11i. High diastereospecificity for PDE5 inhibition was observed in the piperazinedione series with the cis-(6R,12aR) enantiomer displaying the highest PDE5 inhibitory activity. The piperazinedione 12a, tadalafil (GF196960), has been identified as a highly potent PDE5 inhibitor (IC(50) = 5 nM) with high selectivity for PDE5 vs PDE1-4 and PDE6. Compound 12a displays 85-fold greater selectivity vs PDE6 than sildenafil 1. 12a showed profound and long-lasting blood pressure lowering activity (30 mmHg/>7 h) in the spontaneously hypertensive rat model after oral administration (5 mg/kg).

In light of the recent accumulated knowledge on SARS-CoV-2 and its mode of human cells invasion, the binding of viral spike glycoprotein to human Angiotensin Converting Enzyme 2 (hACE2) receptor plays a central role in cell entry. We designed a series of peptides mimicking the N-terminal helix of hACE2 protein which contains most of the contacting residues at the binding site, exhibiting a high helical folding propensity in aqueous solution. Our best peptide-mimics are able to block SARS-CoV-2 human pulmonary cell infection with an inhibitory concentration (IC50) in the nanomolar range upon binding to the virus spike protein with high affinity. These first-in-class blocking peptide mimics represent powerful tools that might be used in prophylactic and therapeutic approaches to fight the coronavirus disease 2019 (COVID-19).

Starting from ethyl beta-carboline-3-carboxylate (beta-CCE), 1, a modest inhibitor of type 5 phosphodiesterase (PDE5), a series of functionalized tetrahydro-beta-carboline derivatives has been identified as a novel chemical class of potent and selective PDE5 inhibitors. Optimization of the side chain on the hydantoin ring of initial lead compound 2 and of the aromatic ring on position 5 led to the identification of compound 6e, a highly potent and selective PDE5 inhibitor, with greater selectivity for PDE5 vs PDE1-4 than sildenafil. Compound 6e demonstrated a long-lasting and significant blood pressure lowering effect after iv administration in the spontaneously hypertensive rat model but showed only moderate oral in vivo efficacy.

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RIP1 kinase regulates necroptosis and inflammation and may play an important role in contributing to a variety of human pathologies, including inflammatory and neurological diseases. Currently, RIP1 kinase inhibitors have advanced into early clinical trials for evaluation in inflammatory diseases such as psoriasis, rheumatoid arthritis, and ulcerative colitis and neurological diseases such as amyotrophic lateral sclerosis and Alzheimer's disease. In this paper, we report on the design of potent and highly selective dihydropyrazole (DHP) RIP1 kinase inhibitors starting from a high-throughput screen and the leadoptimization of this series from a lead with minimal rat oral exposure to the identification of dihydropyrazole 77 with good pharmacokinetic profiles in multiple species. Additionally, we identified a potent murine RIP1 kinase inhibitor 76 as a valuable in vivo tool molecule suitable for evaluating the role of RIP1 kinase in chronic models of disease. DHP 76 showed efficacy in mouse models of both multiple sclerosis and human retinitis pigmentosa.